68 BULLETIN OF THE 



In the suborbital, Scoliodon and Prionodon have a curve that reaches 

 upward in front of the orbit. This curve goes farther forward than the 

 eye in the greater number of the Sharks ; it lies under the orbit in 

 Isurus, Alopias, Cestracion, and Acanthias ; it is absent in Hepta- 

 branchias, Somniosus, and Chlamydoselachus ; and it goes forward of 

 the nostril in Ginglymostoma. 



Between the nostril and the median, in much the greater number of 

 cases, the nasal canal is bent forward ; this bend is either absent or 

 faint in Isurus, Odontaspis, Alopias, Heptabranchias, Chlamydoselachus, 

 Scylliorhinus, and Ginglymostoma. On Isurus the nasals meet the 

 augulars ; on others, as on certain Batoids, they meet the subrostrals. 



A union of the nasals in front of the mouth on most of the sharks 

 forms the median ; no such union takes place on Acanthias, Hepta- 

 branchias, Chlamydoselachus, or Pristiophorus. 



No connection between prenasals and rostrals appears in Heptabran- 

 chias and Somniosus. 



Most often the jugular is directed toward the middle of the first 

 branchial aperture ; Alopias differs in having this tube pass below the 

 gill opening. 



The oral is continuous behind the mouth in Ginglymostoma ; it does 

 not meet the angular in Scoliodon, Prionodon, Triacis, Mustelus, Scyl- 

 liorhinus, Acanthias, and Rhina ; and it was not found in Heptabran- 

 chias, Somniosus, and Pristiophorus. 



A general characteristic of the Batoids is seen in the pleural canals. 

 At once on passing from the Pristiophoridae of the Sharks to the Pris- 

 tidse of the Skates these tubes become prominent features. 



The Pristidse are affected by an excessive elongation of the rostrals 

 and prenasals. Their pleurals are comparatively short, extending but 

 little on the pectorals. The scapular branches are few, but one, a post- 

 pleural, being present in the species sketched. 



On the Bhinobatidaj post-pleural branches are more numerous. In 

 general there is considerable resemblance between this family and the 

 preceding. The anterior cephalic canals are shorter, and there is a 

 sternal canal below the coraco-scapular arch. 



All the Raiidae are marked by greater extension of the upper pleu- 

 rals on the pectorals. A strong branch extending back on the middle 

 of these fins is apparently common. The prominent narrow fold in the 

 subrostral varies in the different species : in Uraptera the fold has 

 been so much narrowed as to bring its sides together. On the ventral 

 surface of Rata ocellata the pleurals are obsolete. 



