NATURAL SCIENCES OF PHILADELPHIA. 493 



region, with its margin rounded, and thence declining very obliquely back- 

 wards to the mouth. 



Eyessubmedian or anterior, without nictitant membranes. 



Mouth inferior, ample and arched in front. 



Teeth in the lower jaw compressed, transverse and acutely multicuspid ; in 

 the upper dissimilar. 



Nostrils inferior, provided at the upper front or margin with a small flap. 



Spiracles, small. 



Branchial apertures all in advance of and dissimilar in size to the pectoral 

 fins; in the known species there are six or seven on each side. 



Dorsal fin single, angulated and produced toward the anterior angle, acute 

 at the posterior above or in advance of the anal ; first obsolete. 



Anal fin present, similar in form to the dorsal. 



Caudal fin heterocercal ; the vertebral lobe is moderately elongated, and has 

 beneath near its end a small triangular lobe ; the inferior basal lobe is mode- 

 rate or small. 



Pectoral fins moderately developed, rounded at each end produced towards 

 the external. 



Ventral fins normally developed, inserted as near or nearer the head than the 

 tail, rounded at the anterior and acute at the posterior or inner angle. 



The family of the Notidamids is distinguished from all others of the order by 

 the absence of the first dorsal fin. The inci'eased number of branchial aper- 

 tures, the dentition, common to all of its known species, and the form of the 

 head and body support the claims of the group to family rank. The situation 

 of the branchial apertures in front of the pectoral fins recalls a character of the 

 Lamnoidse, a family including the Porbeagle, great white shark and basking 

 shark. 



Genus NOTORHYNCHUS, Ayres. 



Notorhynchu3 Ayres, Proc. California Academy of Natural Sciences, vol. i. p. 



72, 1855.' 

 Heptanchus, sp. Midler and Henle, Gray, Oirard, Gill. 



Body depressed over abdomen, thence becoming subcylindrical and taper- 

 ing backwards. 



Dorsal line conspicuous. 



Head oblong, depressed and ovoid above, with the snout wide, and with its 

 periphery transversely rounded, but more or less constricted at the nasal 

 region, and very prominent. 



Eyes moderate, over or in advance of the middle of the side of the jaws. 



Nostrils at horizon of eyes, more or less in advance of mouth, oblique and 

 with a small triangular flap on the hiader margin. 



Teeth of the upper jaw chiefly developed at the front on each side of the 

 symphysis (2 3) simple, acute and curved outwards, or rectilinear with the 

 bases increasing outwards as the teeth severally recede from the symphysis, 

 first (1 2) assuming a smaller external pointed cusp and thence becoming still 

 wider and pectinated on their obliquely declining margins on the outer side 

 of the greater ctisp ; those at and near angle formed by the front and side of 

 jaw bone serrated, and one or two small cusps on the inner ascending margin 

 of the greater one ; teeth of the laterals of the jaw rather abruptly decrease in 

 size. Teeth of the lower jaw uniform, broader, each obliquely diminishing in 

 height outwards, digitated by oblique cusps decreasing from the first, which 

 is minutely serrated on its ascending margin ; median unpoised tooth small, 

 with no median cusp but two or more directed outwards. 



Dorsal fin moderate, acutely angulated at its posterior angle and obliquely 

 emarginated above. 



Anal fin about as large as dorsal, rather further behind, but partly under it, 

 with the anterior angle less produced. 



1862.] 



