316 PEOCEEDINGS OF THE ACADEMY OF [1888. 



drawn in very close limits by Mr. Lyman in his several memoirs, 

 vary materially within the limits of the same individual, and render 

 the discrimination of species which have been most "elaborately " 

 defined as to exact lengths and breadths of the arm-shields and oval 

 plates, the precise form and number of the arm spines, etc., a mat- 

 ter of almost hopeless possibility. 



OpMocoma crassispina, Say. 



One specimen, taken at low water from the North Rock, which 

 agrees perfectly with the species described by Say from the coast of 

 Florida (Journ. Acad. Nat. Sci., Phila. v, p. 147). This species is 

 generally considered to be identical with the Ophiocoma ( Ophiurd) 

 echinata of Lamarck, but I am disposed to consider this identification 

 erroneous, unless, indeed, several distinct forms, as has been averred 

 by Miiller and Troschel (System der Asteriden, 1842, p. 98), were 

 included by Lamarck in his species. Two distinct forms, closely re- 

 lated to each other, certainly do occur in the West Indies, one of 

 which, with more blunt arm spines, is dearly Say's species, wdiile the 

 other, with more elongated arm spines, and much less stoutly 

 developed uppermost spine, more nearly corresponds to the general 

 type of Lamarck's species. 



Ophiocoma pumila, Liitkcn. 



A fragmentary specimen ; exact locality unknown. This species 

 had been recorded by the Challenger from Bermuda. 



OpMostigma isacantha, Say. 



Two very young specimens, dredged in Harrington Sound. 

 Ophiactis Krebsii, Liitken. 



0. MuUerl, Lfitken ? 



Two very young specimens, dredged on the north shore between 

 Bailey's Bay and Shelly Bay, which manifestly belong to one or the 

 other of the above species, although partaking of the characters of 

 both. They agree with 0. Krebsii in having a lobe to the outer edge 

 of some of the upper arm plates, and in the banded character of the 

 arms, while they differ from that species in having but four arm 

 spines. In this respect they agree with 0. Mulleri. Possibly the 

 two species are only varieties of the same form. 



Ophionereis reticulata, LUtken. 



Very abundant at low tide ^i the rock shelters of Shelly Bay ; 

 also under stones at the entrance to Harrington Sound. 



