NATURAL SCIENCES OP PHILADELPHIA. 149 



but smaller, and its hinder half is over the anterior two-thirds of the anal, 

 with the posterior angle of which its own is co-terminal. (The caudal fin, 

 from the front of the lower lobe to its point, equals the distance between the 

 snout and the interval between the third and fourth branchial apertures ; its 

 terminal lobe little exceeds a fourth of its length, and is squarely truncated 

 behind ?) The ventral fin has its outer margin, from the base to the angle, 

 about as wide as the width from that angle to the posterior point. The 

 length of the rostral plateau in front of the jaw equals the width between 

 the outer margins of the nostrils and the interval between the corner folds of 

 the upper jaw. 



D. 18 | 17. A. 18. P. 22. 



This species is distinguished by the proportions of the snout, the more 

 acutely prolonged posterior angles of the dorsal and anal fins, and perhaps 

 the form of the terminal lobe of the caudal ; but it is probable that the latter 

 is worn, and consequently the statement of the length of the fin and the form 

 of the posterior lobe must be accepted with reserve. The number of cartila- 

 ginous rays found after dissection of the skin is less than in the European 

 species. 



A single adult specimen was obtained by Dr. Stimpson at San Francisco, 

 during his visit to that city as a member of the Scientific Corps of the North 

 Pacific Exploring Expedition. 



From Panama, the Institution has received several specimens of a closely- 

 related species, distinguished by the projection of the posterior angle of the 

 first dorsal fin to the vertical of the origin of the ventrals, although the an- 

 terior fourth of the base of the fin is above the pectoral. The caudal fin 

 equals the distance between the snout and third branchial aperture, and its 

 terminal lobe nearly equals a third of the length, and is obliquely truncated 

 behind. The species may be named Mustelus dorsalis. 



These species are interesting as being the first species of the genus found 

 in the Pacific waters of America. The Mustelus felis of Ayres is a species of 

 Triads ! 



Family NOTIDANOID^E, Owen. 



Genus NOTORHYNCHUS, Gill (ex Ayres). 



In the year 1855, and in the first volume of the Proceedings of the " Cali- 

 fornia Academy of Natural Sciences" (p. 73), "Dr. Win. 0. Ayres exhibited 

 a specimen of a shark of a new generic type, with the following description" 

 of the genus 



"NOTORHYNCHUS, Ayres. 



"Dorsal fin single. Branchial apertures seven on each side. Spiracles 

 two. Nostrils double, subterminal. Snout broad, depressed. Tail much 

 elongated, with the fin beneath. Teeth in several rows, those of the lower 

 jaw flattened, arched, serrated ; those of the upper jaw of diverse forms, the 

 middle ones slender, the outer ones approximating those of the lower jaw in 

 form." 



He remarked, that "the shark here described presents, certainly, a very 

 singular grouping of characters. The only genus with which it can be com- 

 pared is Cuvier's Notidanus, previously separated by Rafinesque under the 

 name of Heptranchias, both founded on Lacepede's Squalus cinereus. With this 

 our type agrees in the remarkable feature of a single dorsal Jin and seven 

 branchial apertures. But in Notidanus the teeth of both jaws are represented 

 as similar inform, and the muzzle pointed, the existence of spiracles being as- 

 serted by the one author and denied by the other. We have also in our fish 

 the tail almost as much elongated as in Alopia*." 



The characters attributed to the genus Notorhynchus are common to all the 

 1864.] 



