b DEEP-SEA FISHES OF THE ATLANTIC BASIN. 



KEY TO THE ORDERS OF SELACHII. 



I. Trunk more or less cylindrical, gradually tapering into the tail; gill openings lateral . .. .Sqcali (Sharks) 



II. Trunk depressed (in typical genera the highly developed pectoral fins forming a broad flat disk) ; gill 



openings ventral Rale (Skates and Rays) 



Order SQUALL 



The Sharks. 



Selachians, with body more or less cylindrical (sometimes much depressed anteriorly), 

 gradually attenuating into the tail. Branchial openings lateral, slit-like, ">-7 in number, either 

 entirely iu front of or entirely behind the pectoral, opening over their bases. Pectorals 

 moderately developed, distinctly differentiated from the sides. 



KEY TO THE DEEP-SEA FAMILIES OF SQUALL 



I. Anal iiu lacking. 



A. No spines in front of dorsal tins SCTMNORHINID.E 



1!. Each dorsal tin preceded by a spine Spinach >.e 



II. Anal (in present . 



A. Dorsal fins two. without antecedent spines, the first above or behind the ventrals Scyli.hii.e 



B. Dorsal fins two. without spines, the first in advance of ventrals; caudal crescentic, with a keel on 



each side of its stem; gill openings enormous CKTORRINnxa; 



('. Dorsal fin single, without spine ; caudal without notch posteriorly ChlamydosblachidjE 



In this key only those families are included representatives of which have actually 

 been taken at great depths. Other forms, such as Selache maxima, probably sink below the 

 hundred-fathoms limit at times. Canestrini records as living « /„ luoghi prqfondi, n bathe Med 

 iterranean, Nbtidanus griseus, Heptanchus cinereus, Selache maxima, and Garcharodon Hon- 

 deletii. Spinax niger, however, Scymnus lichia, and Lcemargus rostratus, which dwell "« 

 grande profondita" appear to be the only Mediterranean forms entitled to admission in this 

 list, except perhaps Centrophorus granulosus, which it may be strays in from the deeps of the 

 Atlantic, as far east as Sicily, and Echinorhinus. 



Family SCYMNORHINID^E. 



Scymnidw. Gill, Johnson"s Cyclopaedia, tv, 158. — Jordan and Gilbert, Bull, xvi, U. S. Nat. Mas., 1X83, 13. 

 Spinacida (in part) (it xthkr. Cat. Fish. Brit. Mus., viii, 425-429. 

 ScymnorMnidw, Gill, ms. 



Scymnoid selachians, without anal fins and with spineless dorsals. Scales generally 

 developed in the form of shagreen or fine bristly spines; head oval, depressed; eyes 

 without nictitating membranes; nostrils with a simple anterior tag; mouth inferior and 

 somewhat arched; teeth with trenchant edges; branchial apertures five, in advance of the 

 pectorals; dorsals two, spineless, the first in advance of the ventrals, the second far behind; 

 anal lacking; pectorals rather small: ventrals placed far back. (Gill.) 



KEY TO THE GENERA OF SCYMNID.E. 



I. First dorsal in advance of ventral. Lower teeth erect, triangular Scymnorhinus 



A. Dorsal tins similar iusize. Lower teeth oblique, quadrate, with horizontal cutting edges.. SOMNIOSUS 



B. Second dorsal longer than first. Upper teeth small, conical. Lower teeth larger, triangular, some- 



what oblique [Ecprotomichi's. — Indian Oceau.] 



II. First dorsal opposite ventrals. 



C. Teeth equal iu both jaws, large, very oblique, each with several small cusps. Skin with irregularly 



placed ron ml osseous tubercles and prickles Echtnobhinus 



D. Lower teeth much larger than upper, erect, not serrated. Skin granular. 



[Isistios. — South Pacific and Gulf of Guinea.] 



This family is not common in American waters. Of the three genera occurring in the 

 Atlantic, one, Scymnus, has been found only iu the Mediterranean and the adjacent parts of 



