500 ox THE FAUNA AND BOTTO.M-DEl'OSITo NEAK THE 30-FM. LINE 



taken on ihe various gravel grounds west of the Eddystone, but on these 

 latter the valves are generally separate, old, and worn. From what we 

 know of the habits of the species in other localities the conclusion seems 

 justified that the animal really lives on the fine sand (Grounds I., II., 

 and VI.), but that it lives too deeply buried in the sand to be captured 

 by the dredge. 



Di.sTRinrTiON. Geographical. Greenland, Scandinavia, British and Frencli Coasts, 

 Mediterranean, and Canaries (Jeffreys, No. 55). 



Depth. 5-100 Itithoms (Jeffreys). 



Bottom-deposit. Forbes and Hanley (No. 2.*^) give mnddy ground, sandy mud, and 

 muddy gravel. Metzger (No. 77), in the Pommerania dredgings, records young living 

 specimens (10-15 mm.) on sandy mud and empty shells on fine sand. Heincke (No. 39) 

 states that large empty shells are frequent on muddy ground, on which small living 

 specimens are geuorally taken. In the Liverpool district fresh, large shells are abundant. 

 An immense number of shells and some live specimens were thrown up at Southport, 

 where the shore is sandy, in January, 1891 (No. 40, Vol. VI., p. 110). 



Two species closely allied to Cardium ccJiincUum have been distin- 

 guished by conchologists, namely, C. aaUcatum and C. tuberculatum. 

 The three species are said to differ somewhat in the relative proportions 

 and solidity of the shell and in the length of the spines. These latter, 

 which furnish the most characteristic distinguishing features of the 

 three species, are long, curved, and sharp in C. aculeatam, short and 

 stout in C. echinattcm, and more like tubercles in C. tuhcrculatum. 

 With regard to the habits of the two latter species the following quota- 

 tion from Mr. A. E. Hunt's paper (No. 54) on " The Influence of Wave 

 Currents on the Fauna inhabiting Shallow Seas" is important: — "The 

 large cockle, Cardium acideatum, is abundant in fine muddy sand off" 

 Paignton in Torbay. In this deposit the long spines of this species are 

 of service to increase its holding powers. An allied species, C. tuhcrcu- 

 latum, whose shell is rough and ribbed but not spined, dwells in hard 

 sand at and below low-water mark off the same place. The two species 

 are not commonly found living together, though I have found specimens 

 of C. aculcatum that had been washed in from sea, and their spines 

 denuded in the process, living side by side in hard ground with C. 

 tuhcrculatum. In both these species the rough shells tend to prevent 

 the molluscs being readily dislodged by the waves. Each species keeps 

 to the ground best suited to it. The spines of C. aculcatum would 

 apparently be too great an impediment in burrowing in the hard sand, 

 whereas the spineless shell of C. tuhcrculatum would afford insullicient 

 hold in the soft sand. A very slight advantage from form or sculpture 

 might be ot' great importance in saving the cockles from local extinction ; 

 for in the case of Torbay the struggle for existence is so severe that both 

 species are occasionally washed on shore in suflicient quantities to be 

 carted away for manure." 



Curdiuut cchinaluni is an intermediate form standing between 0. 



