308 PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 



ward, a marked and constant difference from the preceding genus. The 

 mandible has a short horizontal ramus and a short predental beak, which 

 is narrower and more pointed than in Schisniotheriiim. Ameghino has 

 called attention to a remarkable feature of the mandible in this genus and 

 its allies, viz., the division of each horizontal ramus into two elements 

 which are suturally connected. "En outre, dans certains genres (Pele- 

 cyodon, Metopotherium, etc.) les branches mandibulaires sout formees par 

 deux pieces distinctes, une antrieure et 1'autre posterieure ; ces deux 

 pieces sont unies par une suture qui part du bord alveolaire, a peu pres 

 vers la moitie de la longeur de la serie dentaire, et se dirige obliquement 

 en arriere et en bas pour se terminer dans le bord inferieur a peu pres au- 

 dessous de la derniere dent. Cette suture, qui sans doute estun caractere 

 herite des reptiles, disparait de bonne heure ; pourtant, dans quelques 

 especes, elle est persistante " ('94", 141; 160, fig. i). It is true that an 

 appearance of such a suture maybe observed in certain mandibles, but the 

 appearance is not conclusive or convincing. At all events, it cannot well 

 be an inheritance from the reptiles, for in that group the dentary bone is 

 not divided. 



The skeleton of the present genus is incompletely known and only in 

 connection with P. arcuatus. The cervical vertebrae are small and lightly 

 constructed, otherwise differing little from those of the smaller species of 

 Hapalops. The trunk vertebrae are remarkable for the short, slender, 

 backwardly directed neural spines, which are of curiously uniform length 

 and thickness throughout the series, though becoming somewhat longer 

 in the posterior thoracic and lumbar regions. The humerus resembles 

 that of Hapalops, except that the deltoid area is less developed than in any 

 of the other known Santa Cruz Gravigrada ; the ulna is short and slender 

 and in the manus digits IV and V are more reduced than in any other 

 contemporary genus of the order. The femur differs from that of Analci- 

 morfitiusa.nd Schismotheritim in having the broad, antero-posteriorly com- 

 pressed shaft, but has an unusually small third trochanter ; the tibia resem- 

 bles that of Hapalops, except that the astragalar surface is nearly plane. 

 The pes is remarkable for the great size and thickness of digit III, which 

 has a relatively enormous claw ; as in Analcinwrphus, metatarsal IV is 

 but little longer than II and III, while V is much reduced and has no 

 such process from the fibular side of the proximal end as characterizes 

 Hapahps 



