V2i Mr. W. H. Benson on the Genus Camptoceras. 



been a favourite morsel of the wild ducks which haunted the 

 place in the cold season. It may have been more abundant in. 

 the rainy season, during July and August, but the character of 

 the surrounding ground was not then favourable, in point of 

 healthiness or practicability, for exploration. The extermination 

 of an abundant but local water plant, Anacharis Alsinastrum, 

 from a Scottish lake, under the relentless bill of the common 

 Swan, serves to show how the presence of a peculiar foe may 

 influence the propagation of certain species, whether vegetable or 

 animal. 



It is worthy of remark, that no recent species of Physa has 

 hitherto been met with on the continent of India. On the 

 other hand, it seems to be the head-quarters of Lymnaa, many 

 species of which (occasionally of gigantic dimensions) swarm in 

 every stagnant pool throughout the country, accompanied by 

 Planorbis Coromandelicus, Fabr. {Indicus, nobis), and other spe- 

 cies of minute types ; while Ancylus has only been detected in a 

 few waters in the lower ranges of the Western Himalaya, and in 

 the plains at their feet. The other freshwater univalves, con- 

 tained in the same water with Camptoceras, were a large Ampul- 

 laina, two large species of Lymnaa, four species of Planorbis, 

 Melania tuberculata, and some small Bithinics. Although de- 

 ficient on the continent of India, the genus Physa appears in 

 Ceylon, where Mr. E. Layard procured two large species; one 

 of which is ovate and solid, the other much lengthened and acu- 

 minate, being 32 mill, in length by 14 mill, in breadth. It 

 exhibits no symptom of an approach to Camptoceras in its mode 

 of convolution, nor in the form of the aperture, of which the 

 columellar lip is strongly twisted. 



Not having yet published the species of Ancylus above ad- 

 verted to, its characters are now appended. 



Ancylus Verruca, nobis. 



Testa vix sinistrorsa, depressa, subelongato-ovata, poatice vix angus- 

 tiori, laevigata, pallida virente-flavida vel cinerea, tenui, intus albida, 

 submargaritacea, antice superne convexiuscula, postice prope um- 

 bonem breviter declivi, umbone vix elevate, compressiusculo, sub- 

 mediano, ad spatium f totee testae posita. 



Long. ^\, diam. vix 2 mill., alt. 1 mill. 



Hab. ad lacum Bhimtjll Kemaonensem, in palude prope Moradabad, 

 in rivo Rajhera, necnon in rivo Sote, sive Yar Wuffadar dicto, 

 prope Budaon Rohillarum, semper foliis plantarum aquaticarum 

 natantibus adhserens. 



Spa, Belgium, November 30th, 1854. 



Having preserved living specimens of Ancylus Verruca, in a 

 large glass vase of water, among floating water plants, upwards 



