TWO NEW ATLANTIC DOG SHARKS — SPRINGER 467 



or six ridges are present along the middorsal line. In this respect the 

 denticle structure in M. schmitti is intermediate between that of M. 

 canis and that of M. mustelus but closer to that of M. canis. 



ARTIFICIAL KEY TO THE SPECIES OP MUSTELUS 



The key given below will serve only to indicate some of the charac- 

 ters that may be used to separate the species described here from others 

 of the genus. Many of these characters are of doubtful value and 

 must remain so until large series can be studied. The nomenclature 

 of the genus and the North Atlantic species follows the recent con- 

 tributions by Dr. Carl L. Hubbs.' No attempt has been made to 

 distinguish between the white-spotted species in the key, and Mustelus 

 mento Cope and Mustelus nigromaculatus Evermann and Radcliffe 

 are excluded from consideration here, as probably they are not 

 referable to the genus. 



1. Species with white spots of variable size and intensity, per- 

 sistent along the sides where they tend to form an irregu- 

 lar line, and usually generally distributed over dorsal 



surfaces 13 



Species not white spotted; uniform in color or banded or 



spotted with darker 2 



2 (1). Eye small, horizontal diameter of orbit 3 times or more in 



length of snout measured from front of mouth 3 



Eye larger, horizontal diameter of orbit less than 3 times 



in length of snout 5 



3 (2). Color uniform, without transverse dark bars 4 



Color not uniform, dorsal surface with transverse dark 



bars f asciatus (Garman) 



4 (3). Origin of first dorsal in advance of inner angle of pec- 



torals dorsalis Gill 



Origin of first dorsal behind inner angle of pectorals osborni Fowler 



5 (2). Denticles of sides of body (typical denticles from a point 



about equal to horizontal diameter of orbit below origin 

 of first dorsal) with short ridges not reaching more than 

 one-third the distance toward posterior apex, denticles 

 dissimilar in structure on flat surfaces of body, with 

 ridges very strong near middorsal line and weak or 



absent on belly l- 



Denticles of sides of body with longer ridges (see fig. 53) , 

 the central two at least reaching two-thirds or more of the 

 distance toward posterior apex, denticles nearly uniform 



in structure on flat surfaces of body o 



6 (5). Lower caudal lobe of adults not strongly developed, tip 



rounded. 



8 



Lower caudal lobe of adults strongly developed, tip acute_ .- 7 



(6). Origin of first dorsal in advance of inner angle of pectoral 



lunulatus Jordan and Gilbert 



Origin of first dorsal behind inner angle of pectoral, .norrisi, new species 



1 Hubbs, C. L., Scientific names of the American "smooth dogfish," Mustelus canis (Mitchill), and of 

 related European species. Occ. Pap. Mus. Zool. Univ. Michigan, no. 374, 19 pp., 1938. 



