[1920.] NATURAL SCIENCES OF PHILADELPHIA. 201 



The nearly smooth form is selected as typical because it pre- 

 dominates in the lot collected. In some examples no spiral sculpture 

 is visible; others are sUghtly to distinctly striate. The spire is 

 always eroded, even in the smallest taken, diameter 1.3 mm., of 3 

 whorls (fig. 5/), t3ut the summit would be obtuse if perfect, the 

 early whorls increasing the shell rapidly in diameter. At this stage 

 it has the normal shape of Cochlwpa. Later the whorls descend 

 more rapidly, giving it a somewhat Amnicoloid outline. Fig. 5e 

 represents the narrowest specimen found. 



Mutation 'per striata (Fig. 7). Occurring with the smooth and 

 moderately striate specimens there are a few having many strong 

 spiral threads at all post-embryonic stages of growth, as in C. guate- 

 malensis. The largest specimens are of this kind. Alt. 2.7, diam. 

 2.75 mm. 



This species differs conspicuously from C. guatenialensis (Morel.) 

 by its elevated spire. A large series was collected. 



Fig. 7. — Cochliopa izabal mut. perstriata. 



Names Applied to Pachychilus. 



Pachychilus I. and H. C. Lea, Proc. Zool. Soc. London 1850, p. 179, 

 for P. cummingii Lea [ = graphium Morel.]. Not Pachychila 

 Eschscholtz, Zoologischer Atlas, 4tes Heft, 1831, p. 5 (Coleop- 

 tera) . 



Cercimelania Fischer and Crosse, Mus. Sci. an Mex., Moll. terr. et 

 Fluv., ii, p. 327, 1892, type PAiehmanni Phil. 



Glyptomelania F. and C, op. cit. p. 328, type P. glaphyrus Morel. 



Oxymelania F. and C, op. cit. p. 328, type P. schiedeanus Phil. 



Sphaeromelania Rovereto, Atti della Societa Ligustica di Sci. Nat. e 

 Geogr., X, 1899, p. 109, new name for Pachychilus Lea. 



The name to be used for this genus depends upon whether Pachy- 

 chilus and Pachychila are considered to be different names. They 



