26 



XJNITED STATES NATIONAL MUSEUM BULLETIN 294 



in front of the sigmoid process; the anterior pedicle has 

 been broken off at tlic level of the free outer edge of the 

 overarching outer lip. A deep narrow groove intervenes 

 between the sigmoid process and Beauregard's conical 

 apophysis; the latter is a short bluntly rounded process 

 separated by a notch from the thin external portion of 

 the posterior pedicle. The major basal portion of this 

 posterior pedicle projected from the involucrum. 



The involucrum attains its maximum width (pi. 16, 

 fig. 4) behind the projecting sigmoid process and 

 becomes abiiiptly narrowed in front of the level of the 

 attachment of the processus gracilis. Viewed from the 

 ventral side (pi. !(>, fig. 3) this bulla is characterized 

 by an oblique trimcation at both ends; the anterior 

 widening of the tj'mpanic cavity is reflex'ted in the 

 increased width of the anterior end of the bulla which 

 is also greater than the posterior end. 



PERIOTIC 



The type-skull was so badly crushed and broken up 

 prior to excavation that reconstruction has not be«n 

 attempted. Disintegration of the bone has destroyed the 

 original contact surfaces of the larger pieces of the 

 basicranium. 



The posterior process of the right periotic (USNM 

 23636) was firmly lodged between the exoccipital and 

 the base of the postglenoid process of the squamosal 

 before the periotic was detached. This posterior process 

 (pi. 16, fig. 1) is elongate and markedly enlarged 

 toward its distal end, the greatest vertical diameter (84 

 nun.) exceeding the anteroposterior diameter (55 mm.) 

 near the terminal end, although the posterior surface 

 of this process seems to have been abraded before the 

 exoccipital was detached. A well-defined deep and 

 curved groo\e for the facial nerve traverses the ventral 

 surface of this process from its base to its extremity. 

 The pars cochlearis is extended into the large I'ecess 

 behind the pterygoid fossa. 



The external denser pars labyrinthica and its for- 

 ward continuation, tlie anterior proce.ss, are both 

 creased externally and lodged iis usual in the cavity on 

 the internal face of the squamosal. A ventrointernal 

 projection or lip from the pars labyrinthica overlaps 

 the adjacent surface of the scjuamosal and is possibly 

 abnormal although developed on both periotics. The 

 transvei-se diameter of the thick anterior process is 

 rapidly diminished from the level of the pars cochlearis 

 to its blunt anterior end. 



The pai-s cochlearis (pi. 16, fig. 1) is inflated and its 

 external face overliangs the fenestra o\alis. Viewed 

 from the ventral side, its cerebral profile is modified by 

 the projecting dorsal rim of the internal acoustic 



meatus; its convex posterior face descends abruptly 

 below the fenestra rotunda in contrast to the pro- 

 nounced flattening of the ventral surface anteriorly. 



Behind the epitympanic orifice of the Fallopian aque- 

 duct, a narrow raised rim separates the fenestra ovalis 

 from the groove for the facial nerve. The small fossa 

 for the stapedial muscle is rugose. Between the base of 

 the anterior pedicle of the bulla, which is fused to the 

 anterior process, and the epitympanic orifice of the Fal- 

 lopian aqueduct is a shallow depression for lodging the 

 head of the malleus. The small fossa incudis is located 

 on a narrow ledge projecting inward below the groove 

 for the facial nerve. 



The circular internal acoustic meatus (pi. 16, fig. 2) 

 is relatively small, and the upper portion of its rim 

 projects inward at least 15 mm. beyond the level of the 

 cerebral orifice of the vestibular aqueduct located in a 

 deep slit-like depression. The cerebral orifice of the 

 cochlear aqueduct is small. A thin osseous partition 

 separates the large orifice of the Falloi^ian aqueduct, 

 located at the anterointernal edge of the pars cochlearis, 

 from the centrally located internal acoustic meatus. The 

 cerebral face of the pars labyrinthica above and in front 

 of the internal acoustic meatus is depressed, rugose and 

 somewhat nodular. 



Dorsal to the thin shelf projecting outward above the 

 fenestra rotunda and behind the stapedial fossa, a 

 smooth surfaced excavation, presumably for lodging an 

 extension of the air sac system, extends across the 

 posterior face of the pars cochlearis. 



See table 18 for measurements of the right periotic. 



Table 18. — Measurements (in mm.) of right periotic, USNM 



3Sfi36 



Greatest dorsoventral depth of periotic, from most 

 inflated portion of tympanic face of pars cochlearis to 

 most projecting point of cerebral face 63 



Distance between epitympanic orifice of Fallopian 



aqueduct and extremity of anterior process 7o 



Length of posterior process, distance from external end 



to outer wall of groove for faci.al nerve 95 



Distance from external end of posterior process to anterior 



end of anterior process (in a straight line) 179 



VERTEBRAE 



All the vertebrae of this skeleton (USNM 23636) have 

 the epiphyses firmly ankylosed to the centra and with 

 few exceptions all have their processes preserved. Rel- 

 atively minor distortion resulting from crushing is 

 observable on a few vertebrae. This skeleton is repre- 

 sented by 7 cervicals, 12 dorsals, 3 lumbars, and 12 



