6 DEEP-SEA FISHES OP THE ATLANTIC BASIN. 



KEY TO THE ORDERS OF SELACHII. 



I. Tiunk more or less cylindrical, gradually tapering into the tail; fjill ojienings lateral Squali (Sharks) 



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



openings ventral Rai.k (Skates and Rays) 



Order SQUALI. 



The Sharks. 



Sela(;hiiin.s, with body more or less cyHudrical (sometimes much depressed anteriorly), 

 gradually atteuiiatiuff into the tail. Brnnchktl oprii!n</,s lateral, slit-like, 5-7 in luiniber, either 

 entirely in front of or entirely behind the pectural, opening over their bases. I'ectorals 

 moderately developed, distinctly differentiated from the sides. 



KEY TO THE DEEP-SEA FAMILIES OF SQUALI. 



I. Anal tin lacking. 



A. No spines in front of dorsal fins Sctmnorhinid/E 



B. Each dorsal fin preceded by a spine Spinacid.k 



II. Anal fin jiresent. 



A. Dorsal fins two, without antecedent spines, the first above or behind the ventrals Scylliid.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 Cktoriiinid.*; 



C. Dorsal fin single, without spine; caudal without notch posteriorly CHLAMYi)OsEl,A(jHn).K 



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

 been taken at jiicat depths. Oflier forms, such as Sehichc mti.rima, ])robably sink lioldw the 

 bundred-fathonis limif at times. Oanestrini records as living "<« luoyhi profomli,'^ iuthe Med- 

 iterranean, N'otkhiiiKu iiriseus, Heptanchus cinerem, Selache maxima, and Carcharodon Ron- 

 (leletU. Spiiia.v nitjer, however, Scymnits lichia, iuul Lamarriiis raKfrafioi, which dwell ''« 

 (irande profondita,^' a])pear to be the only iMediterranean forms entitled to admission in this 

 list, except perhaps Gentrophorm gramdosuH, which it may be strays in from the deeps of the 

 Atlantic, as far east as Sicil.y, aiul Echinorhinus. 



Family SCYMNORHINIDyE. 



Scymnido'. Gill, Johnson's Cyclopaedia, iv, 158. — Jordan and Gilbert, Hull, xvi, U. S. Nat. Mns., 1883, 13. 

 Spinacida' (in part) GCnther, Cat. Fish. Brit. Mus., viii, 425-429. 

 Scymnorhinida;, 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, depres.sed; 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 tlie 

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

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



KEY TO THE GENERA OF SCYMNID.E. 



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



A. Dorsal fiussimilar insize. Lower teeth i)bli(iuc, quadrate, with horizontal cutting edges. .SoMXiosus 



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



what obliciue [ErPROToMicius. — Indian Ocean.] 



II. First dorsal opposite ventrals. 



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



placed round osseous tubercles and jirickles EeniNiU'.ni.vi's 



1). Lower teeth much larger than upi)er, erect, not serrated. Skin granular. 



[IsLsTirs. — South Pacilic .'ind (!ulf of (iuinea.] 



This family is not common in American waters, of tlie three genera occurring in tlie 

 Atlantic, one, Scymnus, has been found only in the Mediterranem and the adjacent parts of 



