60 Prof. P. M. Duncan on the Salenidae. 



tlve plates. But a new element enters into the composition of 

 the encircling anal ring ; for the right posterior ocular plate is 

 made to fit in between two of the generative plates, and to 

 form no inconsiderable part of it. If this is correct, the form 

 has an atavism greater than that species which A. Agassiz 

 named Salenia varispina^ and which 1 have ventured to rele- 

 gate to the genus Peltastes *j and Sir Wyville Thomson's 

 species, which he considers to be 8. varispina, Ag., has a 

 relic of the genus Acrosalenia of the Jurassic age in its con- 

 formation. 



The Acrosalemce have the right posterior ocular plate within 

 the anal ring ; and this peculiarity is noticed in specimens of 

 all sizes. I have failed to notice it in small and young speci- 

 mens of fossil Salenia. 



Another point of difference between the type of Salenia 

 varispina and the form delineated by Sir Wyville Thomson 

 is the absence, in the last, of whorls of spinules on the great 

 spines ; for in the engraving on page 145 (no. 31) in the 

 ' Voyage of the Challenger ' longitudinal striae occupy their 

 place, and there is a serrate edge to the spines. 



The locality whence the Salenid now under consideration 

 was dredged was (according to Sir Wyville Thomson's book, 

 page 144) to the south-west of Cape St. Vincent, in 1525 

 fathoms. He writes, " There were six specimens of a beauti- 

 ful little sea-urchin with a small purple body and long white 

 serrated spines, somewhat like those of the ' piper ' of the 

 Shetland fishermen {Cidaris hystrix) y 



As there are six specimens, it will be very interesting to 

 know whether they all belong to the form with the ocular 

 plate intercalated. It is to be remarked that Salenia pr-ofundi^ 

 nobis, has a purple colour and that the spines are white : and 

 probably it came from this locality ; but on this point I am 

 not by any means certain. There is some confusion about 

 the number and localities of the Salenice dredged by the 

 ' Challenger ;' for Sir Wyville Thomson writes as follows 

 (pp. 144 and 145, op. cit.) when treating of the characteristics 

 of the Salenidge : — " and I agree with Prof. A. Agassiz, who 

 has referred a specimen of a species either the same as the 

 one we dredged ofi" the coast of Spain or closely allied to it, 

 dredged by Count Pourtales in the Strait of Florida, to the 

 Chalk genus Salenia, under the name of Salenia varispina.^'' 

 Either there was a dredging, the details of which have not 

 been given, " off the coast of Spain," or the dredging of Jan. 

 30, 1873, south-west of Cape St. Vincent, is meant. Proba- 



* Ann. & Mag. Nat. Hist. 1877, xx. p. 246. 



