406 



MEMOIRS OF THE CARNEGIE MUSEUM. 



Contour of Skull compared with the Dentition. 



Contour of Skull. 



Dentition. 



A. No. 1572. Type of D. 

 cooki. Old male. 



B. No. 1841. Paratype of 

 D. cooki. Young male. 



C. No. 1923. Young male. 



Skull symmetrical in the region 

 of the parietals, occiput, zygomatic 

 arches, and palatal regions, but 

 very slightly depressed by crushing 

 in the frontal and nasal regions. 



Horn-cores prominent, nasals 

 blunt and constricted back of 

 horns, frontal region broad and flat, 

 temporal ridges moderately promi- 

 nent, but not united to form a sagit- 

 tal crest, brain-case broad, arches 

 suddenly expanded posteriorly, 

 heavy and rugose on posterior angle. 

 Skull comparatively broad and low. 



Skull somewhat distorted by 

 crushing and otherwise unreliable 

 on account of immature age. 

 Horn-cores incipient, nasals pointed, 

 not projecting over the premaxil- 

 laries, due partly to crushing, a 

 considerable constriction of nasals 

 back of horn-cores; frontals com- 

 paratively narrow and slightly con- 

 vex from side to side, due partly to 

 crushing and partly to immaturity. 

 Temporal ridges less prominent and 

 not united to form a sagittal crest, 

 but quite broadly united with the 

 occiput, brain case broad, zygomatic 

 arches expanded posteriorly and 

 plainly indicating the usual rugo- 

 sities formed in mature males. 

 Skull comparatively narrow, partly 

 due to immaturity and partly to 

 crushing. 



Top of skull more symmetrical 

 than in No. 1841, but considerable 

 lateral crushing has taken place, 

 especially noticeable in the region 

 of the palatines. Base of skull 

 open at suture and basioccipital lost. 



Horn-cores incipient, nasals pro- 

 jecting over the premaxillaries, 

 more than in some specimens, 

 slightly less pointed anteriorly and 

 more constricted back of the horns 

 than in No. 1841; frontals convex 

 hum side to side and proportionally 

 narrow, due to crushing and imma- 

 turity; temporal ridges quite weak 

 especially on right side, not united 

 to form a sagittal crest; brain-case 

 wide, zygomatic arches heavy, indi- 

 dicating that on further develop- 

 ment of the skull the rugosities 

 on posterior angle would be heavy 

 as in old males generally. Skuil 

 comparatively narrow and high. 



Dentition considerably worn. 

 Crista of premi)lars worn off, me- 

 dian valley on P- and P^ isolated by 

 wear, crochet of P- and P'' united 

 with ectoloph, cingulum on P^ quite 

 strong, crochet on P^ not entirely 

 united with ectoloph; crochet united 

 with ectoloph, median valley open 

 and post-fossette isolated on M'; 

 crista slight, crochet heavy, and 

 post-fossette open posteriorly on M-; 

 crista weak and crochet strong on 



Permanent incisors just appearing 

 in the alveoli of the premaxillaries. 

 P' considerably worn, causing the 

 post-fossette to have already become 

 isolated. P- very slightly worn, 

 crista and crochet very slightly de- 

 veloped and not united on tooth 

 of the right side, while that on the 

 left side has crista and crochet better 

 developed and would on much wear 

 form an isolated medifossette; anti- 

 crochet slightly indicated. P' has 

 crista and crochet c^uite well de- 

 veloped and united. P* is well 

 worn, has a small tubercle in the 

 median valley between proto-and 

 mctalophs, crochet well developed, 

 nearly meeting the crista, which is 

 only slightly indicated on the tooth 

 of the right side. M' with well de- 

 veloped crista and crochet nearly 

 meeting to isolate the medifossette. 

 M- just erupted, and shows even less 

 development of crista, but with strong 

 crochet. M^ buried in the maxillary. 



P' in same stage of wear as in No. 

 1841, P- quite simple, no crista, a 

 weak crochet, which on further 

 wear of the tooth would practically 

 disappear; post-fossette very large. 

 P^ not as yet worn, both crista and 

 crochet weak, but showing a ten- 

 dency to unite so as to isolate the 

 medifossette on further wear of the 

 tooth; post-fossette broadly open 

 posteriori}'. D.P'' much worn, me- 

 dian valley nearly isolated by wear 

 of proto- and metalophs; a tubercle 

 of small size in the median val- 

 ley; post-fossette isolated. M' with 

 double, though small, crista; crochet 

 heavy nearly reaching tlie protoloph; 

 post-fossette broadly open poste- 

 riorly. IVP just starting to receive 

 wear, crista extremely weak, crochet 

 stronger than usual. ]VP buried in 

 the maxillary. 



