324 BULLETIN OF THE BUREAU OF FISHERIES 



4. No thorns along mid-zone of disc between eyes and ventrals. 



Barn-door skate, Raja slabuliforis 

 With one or more rows of thorns along mid-dorsal zone of disc behind eyes 5 



5. Posterior third of tail without any large thorns Smooth skate, Raja senta 



Posterior third of tail with one or more rows of large thorns 6 



6. Tail with only one row of large thorns Young Raja scabrata 



Tail with three or more rows of thorns 7 



7. Mid-row of tail thorns very much larger than any other thorns on tail. 



Prickly skate, Raja scabrata 

 Mid-row of tail thorns absent or if present not much larger than other thorns on tail 8 



8. Three rows of thorns on tail Brier skate, Raja eglanteria 



Four or more rows of thorns on tail 9 



9. Length of fish more than 2}i feet Big skate, Raja diaphanes 



Length of fish less than 2H feet 10 



10. Teeth in 70 to 104 rows in each jaw; usually an eye-spot present on each pectoral. 



Big skate, Raja diaphanes 

 Teeth in 38 to 60 rows in each jaw; eye-spot rarely present Little skate, Raja erinacea 



11. No dorsal fins on tail Sting ray, Dasybatus marinus 



Tail with a dorsal fin ir front of spine Cow-nosed ray, Rhinoptera quadriloba 



With regard to the relative abundance of different species of skates on the off- 

 shore fishing banks of the Gulf of Maine, it is of interest that on a trip to Georges 

 Bank (chiefly the northeastern part) in September 1929, aboard the otter trawler 

 Kingfisher, 37 hauls 3uelded from to 105 skates per haul (total 495), as follows: 

 Raja senta, 57; R. scabrata, 325; R. stabulijoris, 42; and R. diaphanes, 71. 



little skate, Raja erinacea Mitchill 



This skate has been desciibed as lacking thorns along the midline; but small 

 specimens 2>){ to 9K inches long and one half-grown specimen of 1Z% inches, recently 

 examined by us, have this row well developed. 



Big skate, Raja diaphanes Mitchill 



Recent investigations have shown that the range of this skate extends north- 

 ward not only to the Gulf of St. Lawrence, as long known, but to the Grand Banks 

 as well, and southward to Virginia. 



The big skate rarely has a median row of thorns except in the very young, so it 

 is of interest to record a female 18 inches long taken near Jeffreys Ledge, November 

 1, 1927, which bears a row of large spines along the midline, from the shoulder girdle 

 to the origin of dorsal on the tail. 



Young specimens of R. diaphanes and R. erinacea, especially the females, are not 

 easily separated from each other by a casual glance, hence the number of rows of 

 teeth which they possess has been an important means of identification. Investi- 

 gators have given various tooth counts ranging from 80 to 110 rows for diaphanes and 

 around 50 rows for erinacea. Several specimens in the Museum of Comparative 

 Zoology, from New England waters, show 70 to 100 rows of teeth on the jaw of 

 diaphanes and from 46 to about 60 rows in erinacea. 



Prickly skate, Raja scabrata Garman 



At the time of publication of "Fishes of the Gulf of Maine" the northern boundary 

 of this skate (widespread in the Gulf of St. Lawrence) was unknown in the open 

 Atlantic. Since then it has been found plentifully on the Grand Banks and reported 

 from the east and north coasts of Newfoundland. 



