ALLEN, EXTINCT OCTODONT FROM PORTO RICO 21 



which is only about half the size of m^. The lower teeth are of nearly 

 equal size, except that the premolar is narrower than the molars, with the 

 anterior third terminating in a narrow projecting terminal angle, and is 

 thus slightly trilobed on the anterior face. 



Scapula. — The scapula resembles that of Capromys piloridesf but is 

 longer and narrower, in correlation with the more slender form of the 

 whole animal (the skull excepted) in Isolobodon. It has a total length 

 of 45 mm., and a breadth at the middle of 24.5 mm. The free end of the 

 spine (acromian process) is nearly as long as the attached portion. (For 

 further details see Plate III, Figs. 1-4.) 



Clavicle. — A single fragment, if identifiable as this bone, is much 

 longer and slenderer than the corresponding bone in Capromys pilorides. 

 It lacks both epiphyses, but still has a length of 26 mm. 



Humerus.— Gresitest length, 45 mm.; diameter of proximal end, 11.5 

 X 9-5 ; transverse diameter of distal end, 11.5 X 5 mm. The supratroch- 

 lear foramen is of medium size and the deltoid ridge is rather strongly 

 developed (Plate III, Figs. 5-7). 



Ulna and radius. — Length of ulna without distal epiphysis, 57 mm. 

 Olecranon process is strongly developed, forming about l/6th of the 

 length of the bone. All of the radii lack the distal epiphyses. The length, 

 minus this portion, is about 46 mm. (Plate III, Figs. 8-14). 



Sacrum. — The single sacrum in the collection is fortunately well pre- 

 served. It consists of four perfectly ankylosed vertebrae and presents 

 nothing of noteworthy importance. It has a length of 51 mm. ; breadth 

 at the proximal end, 31 mm., at the distal end, 15 mm. It is represented 

 in three views, all natural size, in Plate IV, Figs. 4-6. 



Pelvic girdle. — Of the many innominate bones in the collection all are 

 to some extent abraded on their epiphysial borders, but several of them 

 are sufficiently complete to show all of the essential characters. The one 

 chosen for representation in Plate IV, Figs. 1-3, of which three views are 

 given, natural size, indicate its general character. The main axis is nearly 

 straight, not slightly convex dorsally, as in Capromys pilorides. The 

 usual tuberosities are strongly developed. The total length is about 81 

 mm., of which the ilium constitutes about two thirds. Greatest breadth 

 of ilium, 24 mm., of the ischium and pubis, opposite the middle of the 

 thyroid foramen, respectively 9 and 6 mm. The thyroid foramen is large, 

 oval in outline, nearly twice as long as broad, the length in adult speci- 

 mens being about 20 mm. 



« The only pertinent skeletal material available for comparison with that of Isoloiodon 

 is a ligamental, badly diseased menagerie skeleton of Capromys pilorides, to which my 

 comparisons are here necessarily restricted. 



