MARSHALL : ADniTlONS TO BRITISH CONCHOLOGY. 185 



square base. From the same district I have a monstrosity which 

 has only two rows of tubercles ; these tubercles are larger than 

 usual, and oblong ; the shell has 13 whorls, and does not look like a 

 monstrous form, but it corresponds to the var. darkii of Cerithiopsis 

 tubercularis. Another smaller specimen, but mature, has two rows 

 of tubercles on all the whorls except the last, which has the usual 

 three. Forbes and Hanley figure the prevalent British form, Jeffreys 

 a medium one. The two extreme forms — var. obesula Bucq. and var. 

 attenuata Monts. — are found in the Channel and Scilly Islands. 



A fossil species of the Crag, Lieocochlis gnifwsa S. ^^'ood, was 

 dredged by the ' Porcupine' 40 miles N.^^'. of the Shetlands in 345f. 

 (Jeffreys), and also on the Channel slopes in 257-539^ 



Cerithiopsis tubercularis Mont. — There seems to be no doubt 

 that this species is quasi-parasitic, though not invariably so. On the 

 South Devon coast I find them living in the weeds of rock-pools at 

 low water, but quite as commonly under stones, embedded mouth 

 downwards in the integument of compound ascidians, and sticking 

 out like spines, with an occasional Triforis perversa among them. 

 Dr. Tiberi has recorded the same species living in the tunic of 

 Ascidia mentula at Naples, in company with Modiolaria marmorata. 

 The Rev. Prof. Gwatkin writes me in reference to the foregoing : — • 

 " It is particularly interesting to find that C. tubercularis is parasitic. 

 So I had gathered from the peculiar wire-drawn teeth, the mounting 

 of w^hich is most ditificult. The only parallels I know are the Pedicu- 

 larlas and Sistruni spsctriiin, which are both known to live on corals. 

 But the radula of S. spectrum is quite different from that of any other 

 of my Sistrum — a dozen or more .... The other species of 

 Cerithiopsis are unknown to me, but it would be interesting to know 

 whether they have similar teeth." 



Like the last species, C. tubercularis is extremely variable in size 

 and shape. From the Scilly Islands they are particularly varied in 

 form and sculpture. " Occasionally specimens have four rows of 

 tubercles on the lower whorls ; and the apical or top whorls in fresh 

 and perfect specimens, when examined under a microscope, are seen 

 to be very finely and closely ribbed lengthwise."^ The latter char- 

 acter I have not been able to detect. Although the apical whorls 

 are usually abruptly narrowed or pinched up above the spire, in a 

 few cases they are regularly conical with the rest of the spire. 



var. albescens Marsh., yt;?/m. of Conch., 1889, vol. vi., p. 56. — 

 Jersey, Guernsey, Scilly, and Killala Bay. Some of the Scilly speci- 

 mens are bicoloured, the last whorls only being white. 



I Jeffreys, Moll. ' Lightning' and ' Porcupine,' Proc. Zool. Soc, 1885, p. 59. 



