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5. Cyphomyrmex bigibbosus Emery HNS
(Figs. 2, 16, 30, 48)
Cyphomyrmex bigibbosus Emery HNS , 1894: 226-227 (Worker; Brazil: Para). - Kempf, 1959: 216 (Brazil, Amapa: Serra do Navio).
Cyphomyrmex bigibbosus tumulus Weber HNS . 1938: 185-187 (Worker, female, male; Britsih Guiana: Forest Settlement on Mazaruni River; Oronoque River). - Weber, 1940: 413, figs. 7, 11, 12 (Worker, male; British Guiana; Key). - Weber, 1946: 126-128 (British Guiana; Bion.). - NOV. SYN.
Types. - The lone holotype worker of bigibbosus HNS is in the Emery collection at the "Museo Civico di Storia Naturale", Genova, Italy; not seen. Syntypes of tumulus HNS : 3 workers examined (MCZ, NAW).
Worker. - Total length 3.2-3.4 mm; head length 0.75- 0.83 mm; head width 0.67-0.75 mm; thorax length 0.93-1.04 mm; hind femur length 0.83-0.91 mm. Fuscous reddish brown; head usually darkest; mandibles, coxae, femora and sometimes also thorax light brown. Integument, including antennal scrobe, densely granular and opaque.
Head as shown in Fig. 2. Mandibles with 7-8 teeth. Clypeus: anterior border mesially excised; central portion of clypeus obliquely raised towards front, with two acute teeth next to origin of frontal lobes. Vertex with a pair of short carinules. Supraocular tumulus blunt, rounded, not prominent. Preocular carinae reaching the gently produced occipital lobes (Fig. 48), closing completely the antennal scrobe. Lower border of sides of head carinate. Antennal scapes, in repose, not projecting beyond tip of occipital lobes. Only funicular segments 1 and 10 distinctly longer than broad.
Thorax as shown in Fig. 16. Pronotum: the single median tubercle quite distinct, the lateral ones very low and blunt, continued foreward as a faint, often more or less obsolete, margination that separates the pronotal dorsum from the sides: antero-inferior corner acutely dentate. Mesonotum: anterior pair of tubercles prominent and conical, posterior pair very low but distinct and blunt. Mesoepinotal constriction conspicuous but relatively shallow in profile. Epinotum completely rounded and unarmed. Hind femora a little dilated ventrally but not visibly carinate posteriorly at basal third.
Pedicel as shown in Figs. 16 and 30. Petiole in dorsal view rather longer than broad, anterior corners of node not sharply angulate, dorsal ridges at best vestigial, posterior dorsal border without a raised carinule. Postpetiole, in dorsal view, subquadrate not transverse, with a perpendicular anterior face, a rather flat dorsal face, having the posterior border deeply excised between a pair of prominent horizontal tubercles. Tergum I of gaster strongly vaulted, lacking lateral margination and longitudinal carinae. Hairs minute, appressed, glittering, scattered; quite inconspicuous, on body and appendages.
Female. - Total length 3.8 mm; head length 0.84 mm; head width 0.79 mm; thorax length 1.20 mm; hind femur length 0.96 mm. Resembling the worker with the differences of the caste. Differs from faunulus HNS (see below) in the following features: Bicolored, head and gaster fuscous, thorax brown. Occipital lobes much less projecting both in full-face view as in- profile, much as in worker. Midpronotal tubercle faint but still distinguishable. Pair of anterior tubercles between arms of Mayrian furrows very low; scutum laterally not deeply furrowed. Paraptera postero-laterally with a short tooth. Posterior scutellar teeth much shorter, about as long as their width at base. Epinotal teeth completely absent. Pedicel as in worker; petiole elongate, with subparallel sides, anterior corners rather rounded; postpetiole with the same deep mesial excision on posterior border, flanked by prominent lobes, as in worker. Gaster bigibbous on anterior third of tergum I.
Male described by Weber (1938), as of tumulus HNS .
Distribution. - This species is known only from the Amazon valley in Brazil and from British Guiana.
Specimens examined. - Brazil, Amapa Territory: Serra do Navio (K. Lenko) 30 workers (DZSP, WWK); Amazonas State: Manaus (K. Lenko) 1 female (DZSP). - British Guiana: Forest Settlement on Mazaruni River (N. A. Weber) 3 workers (syntypes of C. bigibbosus tumulus HNS ) (NAW, MCZ).
Discussion and synonymy. - Besides the typical form, described by Emery upon a lone worker from Para, Brazil, three additional races have hitherto been proposed, viz. faunulus Wheeler HNS , petiolatus Weber HNS and tumulus Weber HNS . This splitting shows the serious effort of dealing with the undeniable variability cf the species. But the result is nevertheless inadequate, not only from a geographical viewpoint but mainly because the previous authors have seemingly misidentified the typical bigibbosus HNS . Although 1 have been unable to secure the holotype of the latter, I believe that Emery's concise description contains sufficient elements to show that bigibbosus HNS s. str. is identical with tumulus HNS on account of the little drawn out occipital lobes, the acute inferior pronotal angle, the well-developed mid-pronotal tubercle and principally the postpetiole"postice impresso et bituberculato". On the other hand, bigibbosus HNS sensu Weber is really a different form, taking the second oldest name of faunulus HNS , with petiolatus HNS as its junior synonym. On account of the afore mentioned characters, C. faunulus HNS is apparently sufficiently distinct from bigibbosus HNS to be considered a genuine species. It is sympatric with bigibbosus HNS , but occupies, according to our present knowledge, a much greater territory of dispersal.
The head of the bigibbosus HNS worker is strikingly similar to that of strigatus HNS , but the configuration of the thorax, the pedicel and the gaster shows clearly the conspicuous differences between both species.
Variation. - The scanty material available for this investigation is rather uniform. The series from Serra do Navio shows a vestigial lateral margination of tergum I of gaster, which in profile forms an obtuse angle at basal third, as shown in Fig., 16. This condition does not obtain in the series from British Guiana, but is well-expressed in the queen from Manaus.
Bionomics. - Professor Weber made field studies of the present species (" bigibbosus tumulus HNS ") in British Guiana. His account (Weber 1946: 126-128) contains the only available published data and should be consulted by all those that are particularly interested in this subject. Following is a brief resume of his findings:
C. bigibbosus HNS is a rain forest species and seems to prefer high humidities. The nest chambers were found in rotted wood, mostly in excavate cells, but also under bark. The cavity size is variable but averages about 20-25 cc. The fungus garden is mostly sessile, resting on the floor, but variously attached at the sides. Occasionally the chains of fungus garden are also suspended from the ceiling. The substrate is heterogeneous, consisting mainly of yellow to brown particles, often of woody consistency; once even a head of a Dolichoderus HNS ant was used as substrate. Once a worker of Prionopelta punctulata HNS was found inside a nest, preying perhaps on the larvae of C. bigibbosus HNS . The finding of an dealate queen in a tiny fungus garden, with a full grown worker, suggests splitting as a possible means of colony foundation.