MUSEUM OF COMPARATIVE ZOOLOGY. 99 



great deal of curvature. The median is short. The prenasals are long. On 

 each side of the middle behind the lip is an oral that extends but little farther 

 than the corner of the mouth. 



Marked variation in the branches of the suborbital occurs on the specimen 

 sketched. Of species similar in shape, Dasybatus ivalga resembles this one 

 very much in the patterns described by the orbitals, but D. zugei is even 

 more simple than D. dipterurus in respect to the same tubes. In the first case 

 cited the similarity is so close as to raise doubts of the specific distinction of 

 the two. 



Dasybatus dipterurus (Plate XL.). Compared with the preceding, this species 

 shows less prominent scapular curves, sharper bends in the cranials. more 

 connections between orbitals and pleurals and less distance between their 

 points of descent, and a larger number of tubules. On the lower surface 

 the differences are a great deal more pronounced. The pleurals do not 

 reach so far laterally, and they bear tubules toward the sides and posteri- 

 orly as well as in front. The suborbitals traverse a comparatively direct 

 course, though affected by many small flexures, till they reach a point op- 

 posite the mouth, where they turn toward the nostrils, parallel with their 

 former route, and meet the subrostrals directly in advance of the first gill cleft. 

 The subrostrals also are sinuous; they form a prominent loop in front of the 

 nostril, and, apparently, vanish near the base of the rostrum after advancing 

 very little on the nasal valve. There is little doubt that the subrostrals and 

 rostrals join ; the latter pass to the lower surface, and may be traced back half 

 the length of the snout before the walls of the tubes become so thin and deli- 

 cate as to be undistinguishable from the surrounding tissue. The condition of 

 the orbito-nasal in this specimen is one of uncertainty : on one side the subros- 

 tral and the orbital meet, on the other side the subrostral and the nasal join. 



Dasybatus tuberculatum (Plates XLI., XLII.). Differences between this spe- 

 cies and the preceding are numerous, and very noticeable. But a moderate 

 degree of prominence is to be seen in the scapular bends of the laterals. The 

 scapulars and the pre-scapular area are separated. The occipital branch is situated 

 at the end of the aural. An intricate orbito-pleural plexus is formed, in which 

 the spiracular branch of the orbital is concerned, with the usual anteorbital 

 tubules. The tubules are abundant, elongate and branched ; the posterior one 

 on each pleural is forked. Toward the forehead the cranials diverge gradually ; 

 opposite the fontanelle the curves are strong and sharp. Half-way from the 

 eyes to the end of the snout the orbitals pass to the lower surface. On the 

 same transverse line, below the snout, are the points of emergence of both 

 the orbitals and the pleurals, the latter being a trifle farther from the prenasals, 

 although on the top they started down close to the skull. 



Considerable resemblances are seen in the outlines traced by the pleurals on 

 the ventral aspects of the three species sketched, from this genus. There is 

 the same outward prenarial curve, the same course along the anterior border 

 with the great number of short tubules, and a similarly crooked route across 

 the pectorals in the direction of the pelvis. The suborbitals connect with the 



