SUB-CLASS, II— CHONDROPTERYGII. 709 



Sub-class, II— CHONDROPTERYGII. 



Elasmohranchii, Buonaparte. 



Skeleton cartilaginous: no cranial sutures. Prom one to seven gill-openings -. the gills are attached by 

 their outer edges to the skin, and there usually exists an intervening gill-opening with an external orifice 

 between each : none or only a rudimentary gill cover. Three series of valves at the bulbus arteriosus. 

 Optic nerves, although united, do not decussate. Body with vertical and paired fins, the posterior pair 

 abdominal : caudal with an elongated upper lobe. Intestines with a spiral valve. Male sex with prehensile 

 organs attached to the vertical fins. Ovaries containing large ova, which are fertilised, and sometimes 

 likewise developed internally. Embryo with external deciduous gills. No air-vessel. 



This sub-class as at present constituted * is divided into two orders, the first of which does not appear 

 to have representatives in India. 



I. HoLOCEPHAL.\. With only one external gill-opening and a rudimentary cartilaginous gill-coyer : 

 four branchial clefts inside gill-cavity. The palatal and maxillary apparatus coalescent with the skull. 



II. Plagiostomata. With five to seven external gill-openings, and no cartilaginous giU-cover. Jaws 

 distinct from the skull. 



Oedee- PLAGIOSTOMATA. 



Body more or less cylindrical or depressed : the trunk may or may not pass into the tail. From five 

 to seven gill-openings, which may be lateral or inferior. Jaws distinct from the skull. 

 This order has been sub-divided as follows : — • 



Sub-order I— SiiLAchoidei or Sharks. Trunk gradually passing into the tail. Gill-openings lateral. 

 Sub-order II — Batoidei or Skates and Rays. Gill-openings ventral, p. 727. 



SUB-OEDEE, I— SELACHOIDEI. 



Body more or less cylindrical, gradually merging into the tail. Gill-openings lateral. 



GeograpJdcal distribution. — Sharks are found in the seas and estuaries of temperate and tropical regions : 

 some ascend rivers even far beyond the influence of the tides. Not only sharks but saw-fishes occasionally 

 reside in fresh-water lakes, when their return to the sea has been cut off. Professor Meyer (Nature, 

 Dec. 30th, 1875), remarks on this subject, "an accurate comparison (between marine and fresh-water forms), 

 showed no difference at all, and therefore the changed conditions seem to have had no influence on the estei'nal 

 features of the species." 



The sub-order Selachoidei, has been sub-divided into nine families, the following only of which have 

 been recorded from the seas of India. 



SYNOPSIS OP PAMILIES. 



I. Carchaeiidj;. A nictitating membrane to eye : two dorsals and an anal fin, p. 710. 



II. Lamnid^e. No nictitating membrane to eye : two dorsals and an anal fin : nostrils not confluent 

 with mouth, which last is inferior. Spii'acles absent or minute, p. 722. 



III. NoTiDANiD.*. No nictitating membrane to eye : only one dorsal fin and an anal, p. 723. 



IV. ScYLLiiDj;. No nictitating membrane to eye : two dorsals and an anal fin. Mouth inferior. 

 Teeth small, several rows being generally in use at the same time, p. 724. 



* I here omit the consideration as to whether the Ganoids and Dipnoids should he included with the Chondropterygii into one 

 sub-class, PALiKicHTHYES, as proposed. Liliewise I have continued to term this sub-class Choxdroptekygii instead of Elaiiiiohranchii, 

 as is now generally adopted by anatomists. I do so because the formei- designation has the priority. 



