APPENDIX. 327 



Tapes ptjllastea (Venekupis perforans). 

 decussata. 



Clyde Beds. (Smith.) Bracklesham.* (Dixon.) 



Cekatisolen (Solen) legumen. 



Clyde Beds. (Smith.) 



Anatina convexa. 



Irish Drift Beds. (Forbes.) Clyde Beds. (Smith.) 



The woodcut (p. 328) is the representation of a specimen belonging to Mr. Acton, who kindly put it 

 into my hands for illustration as a new species, but I have no doubt of its true position, and it is placed 

 unhesitatingly in specific association with the characteristic shell of the Red Crag. 



This extraordinary individual is the widest deviation from the normal condition of a species that has 

 ever come under my observation, for although it is not very uncommon to see a fresh-water discoidal shell, 

 owing to a Uttle deflection in its spiral, assume a turriculated or conical character, it is exceedingly rare to 

 see an elevated or turriculated shell become depressed into a discoidal form, with its volution upon a 

 horizontal axis. My old friend Littorina littoreus has indulged in extraordinary vagaries, but our present 

 specimen has carried its divergence to an extreme of deformity, emphatically showing that in the practical 

 study of the Univalve Mollusca little real aid is to be derived from any mathematical accuracy in the angle 

 of volution. 



There is, it is well known, an inherent tendency to variation in some species, and this, though not 

 whoUy dependent upon external conditions, may be aggravated by what is unfavorable to a healthy develop- 

 ment. The abnormous forms of Littorina littoreus, Purpura lapillus, and Cardium edule, found in the 

 Estuary Deposits near Norwich, arose, I imagine, from the latter circumstance, as a very large number of 

 individuals in this locality have become more or less distorted ; and as these species in the recent state are 

 rarely eccentric, their deformities were attributed by myself to some extraordinary alteration of the medium 

 in which the animals lived, probably from changes produced by ice or by an excess of outflow whereby the 

 saline properties of the water were prejudicially and suddenly diluted ; but the varieties of a species in the 



was, he says, the opinion of the late Professor E. Forbes, in whose hands they were placed: unfortunately 

 they are not now to be found. 



In the report of the twenty-fourth meeting of the British Association, held at Liverpool, September, 

 1854, p. 78, 'Geol. Sect.,' is a communication by Mr. P. P. Carpenter, respecting some land, fresh-water, 

 and marine shells, obtained by Miss Bright from the depth of one hundred feet in the sinking of a well on 

 the banks of the Avon, at Birlingham, Worcestershire. Among the fresh-water shells is mentioned Limncea 

 fflutinosa ; and with the marine ones are " two minute undetermined Bivalves, quite distinct from any known, 

 either recent or in the Crag. One is an Astarte, very flat and triangular, with sharp ribs like Goiddia 

 Pacijica, C. B. Ad. ; the other is a ? Litcina, somewhat the shape of L. cohimbeUa, with a deeply cut lunule 

 as in Opns, beginning with concentric ridges, then suddenly changing into radiating ribs." 



* Some of the fossils at this locality appear to exceed considerably in dimensions the same species 

 still in existence in our own seas. A specimen of T. denissata, given to me by Mr. Bristow, has attained 

 the length of 3 inches. I have lately seen a fine specimen of Pholas crispata, measuring 4 inches, and am 

 informed they have been found in this Deposit nearly 5 inches in length. 



