COPE.] PALEONTOLOGY MIOCENE PERIOD. 473 



true external series, and do not represent merely a ciugulura. Compar- 

 isons of the molars of the extinct and recent forms are thus facilitated. 



In Chrysochloris and Centetes, according to Mivart, the external cusps 

 are wanting. In the genera in which they are present, as Tupaia, Talpa, 

 Sorex, &c., there are two of the middle series, as in Serpetotherium, and 

 these add a strong internal lobe also. In Erinaceus, they are quadritu- 

 berculate ; but which pair represents the median, I am not yet sure. The 

 closest approximation is made by the genera Potamogale and ^Solenodon, 

 the former African, the latter West Indian. In these, the external cusps 

 are present ; there is but one well-developed median, and in the latter 

 the internal is quite reduced. The molars of Isacis thus resemble most 

 closely those of Solenodon, (Brandt,) but the external cusps are more 

 developed than in that genus. If, as is probable, the superior molars of 

 Urinaceus possess only the outer and median x^airs of tubercles, a resem- 

 blance between the two may be traced: the existing genus differing from 

 Isacis in its two median cusps. The single one of Isacis is connected 

 with the external ones by oblique ridges, as in Urinaceus ; and on one of 

 these is a rudimental tubercle, representing the second median cusp. 



In the lower series, the form of the true molars is not unlike that of 

 several diverse recent genera. It is quite unique in its large four or five 

 cusped last premolar, which has some resemblance to a modified secto- 

 rial. The nearest approach to it which I can discover among recent 

 genera is the Madagascar Galeopithecus. 



In respect to the remainder of the skeleton, numerous characters dis- 

 tinguish it from the Centetidw {which includes Solenodon) and the Potom- 

 ogalidcB. Both of these lack the zygoma, which is present in Isacidw, 

 and have the nasals co-ossified, while they are distinct in ».iese Tertiary 

 forms ; Potamogale further lacks the clavicle. The presence of the zy- 

 goma without postorbital processes is a point of resemblance to Uri- 

 naceus, but the strongly-keeled presternum and absence of cervical neu- 

 val spines are found elsewhere in the Talpidw. In the presence of the 

 humeral arterial foramen, it again differs from Urinaceus and resembles 

 other forms of the order.' 



Thus the afiSuities of Isacis are quite complex, and abundantly indi- 

 cate its position and that of the two allied genera to be in a family dis- 

 tinct from any now in existence. 



Isacis caniculijs, Cope, loc. citat. 



This species is represented by portions of the skeletons of six indi- 

 viduals. All of these lack the anterior teeth of both jaws, while one 

 includes mandibular teeth with vertebrae, ribs, humerus, scapula, pre- 

 sternum, a large part of the cranium, &c. 



The basi-occipital is three-keeled below, and the petrous bone with a 

 longitudinal concavity below. The edges of the outer lobes of the first 

 superior molar are acute. There is no external cingulum, but the diago- 

 nal crest from the median cusp i)asses to the i)Osterior base of the pos- 

 terior outer. There is a short but strong cingulum on the posterior 

 base of the median lobe, which terminates in a small internal cusp. The 

 rudimental anterior middle cusp is on the anterior diagonal ridge, which 

 does not reach the base of the outer anterior cusj). The outer cusp of the 

 last premolar is elongate and compressed ; the inner cusp is small, acute, 

 and opposite the posterior margin of the outer; enamel smooth. The 

 anterior of the two prisms composing the inferior true molars is more ele- 

 vated than the posterior. The crests of each form a V with the obtuse 

 apex outward, and the anterior limb is shorter than the posterior. The 

 last molar is a little smaller, and is produced behind by the addition of 



