The Nautilus. 



Vol.. XXIII. JANUARY, 1910. No. 8 



NEW AMNICOLID^ OF THE PANUCO KIVEB SYSTEM, MEXICO. 



BT HENRY A. PILSBRT. 



In the course of Mr. A. A. Hiiiklt-y's expedition to the Panuoo 

 river region in 1907 he found Potamopyrgiis coroimtus (Pfr.), Paludes- 

 trina tampicoensis Pils., Gochliopa riograndensis Pils. & Ferr., and 

 an Ajnnicola identified as A. guatemalensis C. & F., but which on 

 further study turns out to be a new species. Several more forms 

 are now added by the expedition of 1909, among th^'m a south- 

 western representative of Somatogyrus and some very handsome 

 though small species of Cochliopa. 



In the works of Crosse and Fischer and of von Martens, the 

 American spinose Aranicoloids are referred to the genus Amnicola, 

 in the belief that Potamopyrgus does not occur in America. This 

 idea is in my opinion wholly erroneous. The American P. coronatus 

 (Pfr.) has the dentition and the viviparous reproduction of the New 

 Zealand type of Potamopyrgus. In New Zealand, as in America, 

 both spinose and smooth forms occur. There is no conchological 

 difference. No Amnicola is viviparous, and there is a perceptible if 

 small difference in the shells, which are more compact and more 

 solid in Amnicola. 



The genus Potamopyrgus occurs also in the Antilles, South 

 America, West Africa and Tasmania. Perhaps the British Hy- 

 drobia jenkinsi belongs to this genus. If viviparous it certainly 

 does; but I have not investigated the species. Like Planorbis, 

 Viviparus, Lymrtcea and some other fresh-water genera, it seems 

 that Potamopyrgus has a very wide geographic distribution. Jn 

 female Potamopyrgus one finds the young shells as in the genus 



