MUSEUM OF COMPARATIVE ZOOLOGY. 89 



Rhinobatus. 



Rhinobatus planiceps (Plate XXIV.). From the shoulder girdle to their 

 ends on the tail the laterals of this species are nearly straight. At the pecto- 

 ral arch the scapular curves carry them outward, and back of the head they 

 approach each other. Posteriorly they send numerous tubules outward; ante- 

 riorly others are sent inward and backward. Behind the scapular there are four 

 post-scapulars, each of which has two or more tubules near the end. There is 

 more lateral curvature in the pleurals in this genus than was seen in Pristis ; 

 there is also a more intimate connection between them and the suborbitals, by 

 means of four or more of the tubules. Opposite the forward part of the orbit, 

 about half-way between it and the margin, the pleurals pass through the disk, 

 after sending numerous tubules on the pectoral. These pleural tubules are 

 of two kinds, one stronger, longer, and straighter; another finer, shorter, and 

 crookeder, distributed among the first. The course of the pleurals on the 

 lower surface is short; they meet the jugulars in front of the first branchial 

 aperture. 



The aural curves back in the middle. A slight divergence obtains in the 

 short occipitals. In front of the eye the cranials curve outward sharply; they 

 approach each other nearest along the middle of the rostral cartilage. At the 

 end of the suborbital a branch is sent backward; in front of the eye its tubules 

 extend both inward and outward; and still farther in front they are sent to- 

 ward the margin. Instead of going around its edge, the suborbital passes 

 through the disk very near the border. On reaching the lower surface this 

 tube makes a broad curve back, and joins the subrostral opposite the nostril. 

 A short orbito-nasal connects it with angular and jugular, both of which are 

 short. The nasal is bent back behind the nasal valves. The median is very 

 short. Near the middle of their length the elongate prenasals are curved 

 toward each other. The oral crosses the median line behind the mouth, but is 

 disconnected from the angular. Around the anterior border of the abdominal 

 chamber, beneath the coraco-scapular arch, there is a sternal canal, which 

 differs from the others in being more open; it does not cross the middle. This 

 canal was not seen in Pristis. 



Syrrhina. 



Syrrhina brevirostris (Plate XXV.). A description of the canal system in 

 this species would duplicate that of the preceding, excepting that rostrals, sub- 

 rostrals, and prenasals would be found to be greatly shortened. Other points 

 of difference, less important, are seen in the smaller number of branches of the 

 tubules and the undivided condition of the sternal. A study of the canals 

 of this species discloses little that favors separation from Rhinobatus, since it 

 differs less from species of that genus than some of them do from each other. 



