780 PROCEEDINGS OF THE ACADEMY OF [DeC, 



AMNICOLID^. 

 Pyrgulopsis patzcuarensis Pilsbry. PL LII, figs. G, 7, 8. 



The Nautilus, V, p. 9, May, 1S91 ; Proc. Acad. Nat. Sci. Phila., 1891, p. 330, 



PI. 15, fig. 8. 

 Mission Scient. au Mex., Moll., II, p. 277. 



Lake Patzcuaro, Michoacan, the type locality. This was originally 

 described from mutilated examples. A series of over 60 specimens 

 taken by Mr. Rhoads in 1899 enables me to complete the description 

 and to illustrate perfect shells. All are empty shells, and I am there- 

 fore unable to examine the dentition, to ascertain whether the species 

 is a true Pyrgulopsis or a Potamopyrgus. 



All of the shells agree in having the first two whorls smooth and con- 

 vex. Then a strong median keel sets in, continuing 2^ or more whorls, 

 and there is also a minor keel which may be visible just above the 

 suture or concealed by the next whorl. Both keels usually become 

 weaker, mere angles on the last whorl or more, or they may completely 

 disappear, leaving the whorl rounded. The keel is always even and 

 smooth. There are nearly 7 wdiorls in full-grown shells. The aperture 

 is regularly ovate; the outer lip is sinuous, being retracted above. 

 The largest shell measures, length 7.7, diam. 3.2 mm. 



I have seen some thousands of specimens of Potamopyrgus from Texas, 

 Mexico and Central America, Venezuela and the West Indies, embrac- 

 ing a great variety of forms ; but I have not seen this particular type 

 of shell except from Lake Patzcuaro. It seems to me to be a reason- 

 ably distinct species. The form called Amnicola coronata var. uni- 

 carinata by von Martens' is not an uncommon variation in the spinose 

 Potamopyrgus, and like the smooth, ecarinate phase, it is not a racial 

 or subspecific modification, nor is it sexual, for I have foiuid the 

 unborn young in smooth, carinate and spinose shells, when opening 

 them for the radulse. American species of Potamopyrgus are dimori3hic 

 or trimorphic, like some butterflies, owls, etc. 



The gentis Potamopyrgus is amply distinguished from Amnicola by 

 its viviparous reproduction, Amnicola being oviparous. I fail to see 

 the advantage of lumping them as some recent authors have done. 



Chondropoma martensianum Pilsbry. PI. LII, figs. 4, 4a. 

 Nautilus, XIII, p. 140 (April, 1900). 



^fountains of Poana, Tabasco (Jose N. Rovirosa). Illustrations 

 are now given of the type of this species, which has not before been 

 figured. 



^ Biologia, p. 433, September, 1899. 



