FAMILY CARDIACEA. 



237 



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1. Cyclas rivicola. Brook Cyclas. 



Shell ; oval-globose, tliin, ventricose, compressed towards the ven- 

 tral margin, densely concentrically ridge- 

 striated, bluish white, covered with a dark 

 olive-green glossy epidermis, nearly equila- 

 teral, anterior side rounded, with a faintly 

 impressed lunule beneath the umboes, pos- 

 terior rather produced, slightly truncate, 

 umboes obtuse ; ligament apparent. 

 Tellina cornea var., Schroter (1779), Gesch. Fluss- 



Conch. p. 189. pi. iv. f. 4. 

 Cyclas cornea var., Draparnaud (1801), Tall. Moll. 



p. 105. 

 Cardium corneum var., Montagu (1803) Test. Brit. 



p. 86. 

 Cyclas rivicola, Leach (1818), Lain. Anim. sans vert. vol. v. p. 558. 

 Cyclas sabulicola, Krynicki (1831), JBourg. Monog. Splicer, p. 1 3. 

 Cyclas cequata, Sheppard (1840), Gray, Turt. Man. p. 280. 

 Sphcerium rivicola, Boui'guignat (1853), Rev. Soc. Cav. p. 345. 

 Sab. Central Europe. Metropolitan, Midland, and Northern Counties of 

 England. Neighbourhood of Dublin. (In rivers and canals.) 

 This species, which is more abundant in our metropolitan rivers, 

 the Thames, the Lea, and the JSTew River, than in any other part of 

 the kingdom, is much the largest species of the genus. Its shell is 

 oval-globose, densely concentrically ridge-striated, of a clear bluish 

 white internally, covered externally by a rich glossy olive-green 

 epidermis. The animal is of a fawn-grey colour, the siphonal tubes 

 being tinged with rose or tawny, while the foot is white. 



C. rivicola inhabits many parts of the Continent, including Hol- 

 land, Belgium, Germany, and France, but it is much less widely 

 diffused than C. cornea. It is not found in Scotland, and it is only 

 lately that an Irish habitat, neighbourhood of Dublin, has been 

 attributed to it. It has a very near representative in New Zea- 

 land, in a species of rather smaller size not yet described, collected 

 by Mr. Strange ; and in the United States in Mr. Say's C. similis, 

 inhabiting the muddy banks of the Connecticut. 



The Cyrence, which inhabit the rivers and estuaries of the inter- 

 tropical parts of both hemispheres, are very closely connected with 

 the Cycladce through this species. They are especially abundant in 

 the Malayan islands and peninsulas, where they Live imbedded in the 

 mud of mangrove swamps. 



