12 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY - IV. 



CLASS III -ELASMOBRAXCHII. 



(The Sclachidiis.) 



Skeleton cartilaginous; skull without sutures. Body with median and 

 paired tins; the ventral lins abdominal; shoulder-girdle developed, lyri- 

 form: caudal lin heteroeercal, the upper lobe produced; gills attached 

 to the skin by the outer margin ; gill-openings several, or single leading 

 to >everal clefts; membrane bones not developed, except sometimes a 

 rudimentary opercle; skin naked or covered with minute imbricated 

 scales or hard plates, sometimes spiuous; no air-bladder; arterial bulb 

 with three Aeries of valves; intestine with a spiral valve; optic nerves 

 united by a commissure, not decussating; ovaries with the ova few and 

 large, impregnated, and sometimes developed, internally; embryo with 

 deciduous external gills; males with prehensile introniittent organs, 

 "claspers," ;ii t ached to the ventral lins. Sharks, Skates, and Chimaeras. 

 o7, a plate or blade; Pt' (JL i"/.'- a i gills.) 



ANALYSIS OF ORDERS OF KLASMOBRAXCHS. 



Grill-openings slit-lik.e, 5 to 7 in number; jaws distinct from the skull. (Subclass 



Selachii.) 

 t Gill-openings 1 literal ............................................... S.>r u.i, D. 



it (Jill-openings ventral ......... .. ................................ ..... J.'AI.K, E. 



"* Gill-openings single, leading to lour branehial clefts; jaws fnale.sc.-ut -with the. 

 skull (subclass Holoccphali) ........................... Hoi.. i KHALI. !'. 



SUBCUSS SELACHIL 



(The Shark* <ul Rays.) 



Elasmobranchiates with the gill-openings slit-like, live (rarely six or 

 in iiiimber; jaws distinct 1'rom the skull ; no opereular nor pelvic 

 1 101 lev ; derivative radii sessile on the sides oft he basal bones of the limbs, 

 raids eiiterin- the articulation. 



A>heie understood, this subclass is equivalent to the Plagiostoma/fa of 

 author-, and includes the orders or suborders /,'<//>, the Uays. and X//^r///, 

 the Shark>: -loups which a IT perhaps hardly worthy of ordinal value. 

 (TV//--, a shark, from nit." /_>-, cartilage.) 



()IM)KR I) -SQUALL 



(Tin- N/////-/,-x.) 



(iill ojH'iiin.iis lateral, slit-like, live to seven in number; general form 

 elongate, the body gradually passing into the tail. The typical sharks 



