Quarterly Journal of Couchclogy. 213 



most remarkable feature of this species, is its coating of long 

 spines or hairs, arranged in spiral rows around the whorls, forming 

 the most anomalous and interesting species in the whole range of 

 our freshwater mollusca. That Mr. Lea's type specimen was an 

 old shell, without an op^^rculum, and from which the spines were 

 eroded, is probably true, as, having already published two species, 

 he would have noticed the very distinct opercle, and the hairy 

 spines of the epidermis form a feature, that no naturalist of Mr. 

 Lea's unusual acuteness, would have passed without observation; 

 yet we find no mention made of the very remarkable operculum in 

 any of the species, nor of the hirsute epidermis of T. Coosaeinis. 

 To obtain fine specimens of the latter species, has been very clifti- 

 cult, as the Dlder adults seem to lose the spines by erosion; though 

 if taken in the early autumn, the summer's growth of shell is gene- 

 rally clothed with its proper appendage. All the genus inhabit the 

 Coosa, the T. angulata and T. Coosaensis being confined, so far as 

 I have been able to discover, to the upper and more rapid parts of 

 the stream; while the T. magnifica occurs in the lower parts of the 

 Coosa and in the Alabama proper. I do not deem it by any means 

 improbable that this anon:ialous system of d'"ainage, containing two 

 genera of operculates not found elsewhere in the world, may yet 

 furnish extraordinary riches of knowledge bearing upon the great 

 problem of Geographical Distribution; a problem which I firmly 

 believe will reduce twenty-five per cent of all knov/n species to 

 synonyms. While separating the T. angu'ata for the present, from 

 the T. magnijica. the very fact of their residing in parts of the 

 stream so different, may offer suggestions as to their identity: and 

 the question is not so much whether the same species can exist un- 

 der such varying conditions, as whether the varying conditions do 

 not produce varieties that have been called species. The shells 

 live on the under side of loosely lying rocks and large stones, to 

 which they cling with much tenacity. They are very abundant^ 



