Zoological Society. 353 



frontal and zygomatic processes well-developed, the latter attached 

 firmly to the zygoma ; the supratemporal process rising obliquely ; 

 pterygoid bones compressed, and not inflated ; crotaphite impression 

 approaching near to the occipital ridge ; tj'mpanic bone attached, 

 small, and not inflated ; (immediately in front of the circular facet 

 for the stylohyal bone there descends a strong process, which may 

 probably belong to the tympanic bone and form a portion of a vaginal 

 process ;) lower jaw produced in front, deepened in the middle by the 

 extensive implantation of the molars, the condyle much elevated ; 

 teeth ^j, quadrate, grooved transversely on the crown when worn, 

 the caementum being thickened on the anterior and posterior surfaces ; 

 the posterior upper one small. 



M. CUVIERI. 



Dr. Lund figures a tooth having the characters of this well-known 

 genus, but of smaller size, under the name oi MegatheriumLaurillardi. 



Megalonyx, Jefiferson. 



General cranial characters unknown ; teeth ^^, subelliptical, with 

 a ridge on the inner side. 

 M. Jefersonii. 



Mylodon, Owen. 



Intermaxillary bones small (lost in the skeleton) ; postorbital pro- 

 cess but little developed, thick ; malar bone with the frontal process 

 indicated by a slight angle, the zygomatic well-developed, touching 

 the zygoma, the supratemporal process rising obliquely ; pterygoid 

 bones thin and compressed ; crotaphite impression approaching near 

 to the occipital ridge ; tympanic bone reduced and separate ; (the 

 foregoing characters can of course apply only to the Mylodon robustus, 

 it being the only species of which the cranium is known ;) lower jaw 

 broad and more or less prolonged in front, the lower outline straight, 

 the condyle depressed ; teeth j^, the anterior ones rounded or tri- 

 gonal, the posterior ones larger, trigonal in the upper jaw, gradually 

 becoming bilobed in the lower. The species can only be characterized 

 by the lower jaw, as it is the only part that is known in all of them. 

 The characters are taken chiefly from Prof. Owen's works. 



M. Darwinii. 



Lower jaw much produced anteriorly, with a double mammelliform 

 tuberosity upon the symphysis below. The first tooth rounded or 

 subtrigonal, the second subelliptical, with a slight depression on the 

 inner side ; the third subquadrate, grooved on the inner side ; the 

 posterior internal angle produced ; the fourth bilobed, sharply grooved 

 on the inner side. 



M. Harlani. 



Lower jaw with the symphysis short ; the second tooth sub- 

 quadrate, grooved on the inner side, with the posterior internal angle 



