Mi-.F. U.Gosseonthe Sub-basal Membrane o/Adanisiapalliata. 107 



deciding hastily on any of these small bivalves, without seeing 

 the living animal. This remark applies especially to the P. ni- 

 tidum, which in general form is so similar to the P. pusillum, 

 and in which, when the animal has been suffered to die in the 

 shell, a dark stain arises on the upper part of the valves near 

 the hinge, rendering the umbonal striae, one of the most distin- 

 guishing characters of this species, very difficult to perceive. 

 June 29th, 1858. 



XI. — On the Nature of the Sub-basal Membrane o/ Adamsia 

 palliata. By Philip Henry Gosse, F.R.S. 



The clear brown membrane which covers the greater part of 

 those shells on which the Adamsia palliata is adherent was long 

 ago carefully described by Dr. Coldstream*. Its chemical com- 

 position and its nature were, however, still left undetermined ; 

 and its very origin was, only as a probability, attributed to the 

 Adamsia. It has since been suggested, — though, so far as I 

 know, only conjecturally, no evidence having been adduced to 

 confirm the supposition, — that the membrane in question is an 

 incipient corallum, in which case it might be expected to show 

 traces of a calcareous formation. 



A specimen just sent me from the Clyde has afforded me an 

 opportunity of setting the question at rest. The Adamsia, a 

 mature specimen, was attached to an old worn shell of Trochus 

 ziziphinus. When I obtained it, life had ceased; and though 

 decomposition had not set in, yet the base was beginning to 

 separate from the support. When this separation had proceeded 

 a little further, I found that the basal surface of the body was 

 covered with a thin film of the clear yellow membrane, where it 

 had been adherent to the outer lip of the Trochus. This film 

 was easily detached from the animal ; and this I subjected first 

 to microscopical examination. 



Under a power of 600 diameters, with transmitted light, the 

 membrane showed the manifest characters of an epidermic slough, 

 — a clear, structureless layer, with a multitude of irregular mi- 

 nute granules, a few oil-globules, a good many scattered Cnidee, 

 and some DiatomacerB of various species, some of which were 

 alive and moving actively. Exposed to a red heat, this epidermic 

 membrane became charred, without the slightest shrivelling, or 

 shrinking, or change of form or dimensions. 



The film above described seems to have been a newly-forming 

 structure. When the decomposition of the animal had some- 



* Johnston's Brit. Zooph. cd. 2. j). 208 et seq. 



