MUSEUM OF COMPARATIVE ZOOLOGY. 75 



vergent, more decidedly so in advance of the frontal holder ((J), and they 

 approach each other closely on the thin portion of the prohoscis. As in Chi- 

 maera, the occipitals connect the laterals and the orbitals with the aural and 

 the cranials, instead of connecting the aural and the laterals with the orbitals 

 and the cranials as in the Selachia. Orbitals and jugulars meet below the 

 pupil of the eye. The suborbitals are very long; they pass quite to the end 

 of the snout, and there meet the rostrals as the latter pass to the lower surface 

 of the rostrum. A row of short pieces of canals across the throat serves to 

 unite the jugulars. Under the fore part of the pupil the oral leaves the sub- 

 orbital; it curves forward on the cheek and the chin, and backward behind 

 the corners of the mouth. On the cheek it has what appears to be a more 

 slender tube just in front of itself. Not far in front of the oral the angular 

 descends toward the mouth from the suborbital. As it nears the lip it takes 

 more of a forward course, and, following near the border of the rostral flap, 

 finds its way down and backward to the edge of the lower surface, where it 

 turns under and inward to cross the wing and meet the angular of the oppo- 

 site side. After meeting the suborbital each rostral in its backward route ap- 

 proaches very close to its fellow, under the end of the rostrum, if it does not 

 unite with it. Farther back they diverge, and each turns up a side of the 

 snout, curving back as if to unite with the nasal. The union of subrostral 

 and nasal has not been traced. In the adult specimens the oral and the jugu- 

 lar show tendencies to obsolescence. 



Although there are great differences in the shape of the head in this genus 

 and in Chimsera, in the arrangement of the canals in the two cases there is a 

 great deal of similarity. One has only to suppose the snout of Callorhynchus 

 shortened, so that the flap may be applied against the head, and the union 

 of subrostral and nasal, if not already existing, to produce an arrangement 

 essentially the same as that of Chimaera. 



Scoliodon. 



Scoliodon terrce novm (Plate V.) represents one of the subdivisions of the 

 genus Carcharias, as arranged by Midler and Henle. Comparison of this spe- 

 cies with Prionodon milberti, a representative of another of these subdivisions, 

 will give an approximate idea of the range of variation within that genus. 



A small amount of curvature only is to be noticed in the thoracic portions 

 of the laterals. Below the second dorsal they make a slight descent, then 

 they rise rather higher than before, after which the canals retain the same rela- 

 tive height as regards the vertebral axis till they reach their terminations at 

 its end. 



In its middle the aural has a shallow backward bend ; and it has one ox 

 similar depth in the opposite direction near each end. The occipitals are 

 comparatively long; they are extended obliquely out toward the eye. A short 

 distance from these canals, each cranial makes a short but decided outward 



