BY ALLAX R. MCCULLOCH. 



465 



specimen e\'idently referable to D. thctidis, which has an unbroken row of about 

 fifty tubercles between its anterior end and the caudal spine, of which ten are 

 in advance of the scapular region. The accompanying figure (Test-fig. 3) is a 

 sketch I made of a large female, 70 inches wide, which was trawled by the 

 "Endeavour" in sixty fathoms East of Babel Island, Bass Strait, and which 

 was thrown overboard after I had made notes upon it. The disc was smooth 

 above, except along the median portion, where there were several rows of large 

 tubercles bearing spines; a few tubercles were close to the snout, and a few 

 more midway between the snout and the eyes; in front of and above the eyes 

 were others which differed in number on each side; twenty inches behind the 

 snout and well behind the level of the spiracles a median row of tubercles 

 commenced, which was supplemented on the shoulders by some parallel spines; 

 behind the middle of the disc the tubercles were arranged in four irregular 

 rows which were gradually reduced to two at the level of the ventrals. The 

 tail was intensely spiny, and there was a narrow fold on the under surface 

 from the level of the caudal spine to its end, about half an inch wide; the 

 tail was forty-six inches long but incomplete. The teeth were without cusps. 



Synonymy.— GuTmaji (Mem. Mus. Comp. Zool., xxxvi., 1913, p. 383) has 

 included D. thetidis in the synonymy of his D. latus and the two species are 

 certainly very similar. But the tail is more than twice as long as the body in 

 latus and is apparently less spiny than in thetidis, in which it is not much 

 longer than the disc. It is improbable also that a species occurring in modera- 

 tely deep water off the south-eastern coast of Australia should be identical 

 with a species from the warm waters of the Hawaiian Islands. 



Ogilby (Mem. Austr. Mus., iv., 1, 1899, p. 46, and Proc. Roy. Soc. Qld., 

 xxi, 1908, p. 8) has suggested that the specimen recorded by Giinther (Brit. Mus. 

 Cat. Fish., viii., 1870, p. 480) from Sydney as Trygon tuberctilata is rcicrahlc to 

 Dasyatis thetidis, but it is more probably an example of D. fhiviorum Ogilby. 

 Giinther described the tail as more than twice the length of the disc, and usually 

 provided with a dorsal as well as a ventral cutaneous fold; the spines on the tail 

 were said to be minute. In all these characters the specimen differs from D. 

 thetidis while agreeing with D. fluvionim. 



D. thetidis differs from 1). hrevicaudatus in the following characters: 



A. Disc with more or less numerous spinate tubercles on the middle of the 

 back. Eyes not closer together than the spiracles. Internasal space shorter 

 than the distance between the nostrils and the end of the snout; outer 

 angles of internasal lobe rounded. Tail longer than the disc; a narrow 

 cutaneous fold on its lower surface extending liackward to its tip. Tubercles 



and spines large ! thetidis 



AA. Disc entirely smootli, witliout spines on the back. Eyes closer together 

 than the spiracles. Internasal space almost equal to the distance between 

 the nostrils and the end of the snout ; outer angles of internasal lobe pointed. 

 Tail shorter than the disc: a cutaneous fold on its under surface which 

 terminates below the end of the spine. Tubercles and spines 

 smaller hrevicaudatus. 



Occurrence. — B. thetidis and B. hrevicaudatus are ajiparently common in 

 depths down to sixty fathoms ofl the coast of New South Wales where they 

 are taken by the State trawlers, and find a ready sale as Black Skate. I have 

 also seen them trawled off the eastern coast of Tasmania, one or more occun-ing 

 in each haul of the net, but the differences between the two not having been 

 recognised, nothing is known as to which species is the most abundant. 



Locality.— Off Norah Head. New South Wales, 20-40 fathoms; coll. F. 

 McNeill. June. 1921. 



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