THE NAUTILUS. 123 



carefully given with sufficient force to dint the surface without 

 breaking the substance of the shell. These dints are sometimes 

 quite regular in arrangement and frequently have the aspect of 

 zones following the basal and previous whorl transversely and par- 

 allel to the sutural line, like so many flat bands. 



This form of sculpture is also met with not only in related groups 

 like the Physas, often conspicuously shown in the form to which the 

 late Dr. Lea gave the name of P. Carltoni as well as in other s])ecies 

 of the same genus ; frequently in Planorhis and Carinifex as well 

 as in the river-snails Avipullaria and in the Bulimi among the 

 land shells. 



Third. Another and not infrequent aspect of sculpture is exhib- 

 ited by several species, and consists of fine close set incremental 

 lines crossed by transverse, somewhat waved and slightly incised 

 grooves ; the same character of sculpture is not infrequent in many 

 terrestrial pulmonates. The Mexican Glandinas, for instance, fur- 

 nish in several species, beautiful examples of this delicate tooling of 

 the surface, to use a familiar mechanical term. 



j\Ir. Dall recently collected several specimens of Limncea palustris 

 in the irrigation ditches near the Hot Springs in Honey Lake Valley, 

 Lassen Co., California, (within the area of the extinct tertiary Lake 

 Lahontan), which exhibit this form of sculpture markings. It is 

 often if not generally present in the following species: 



LimnaPM lepida Gould, Limncea ampla Mighels, Limncea Sumassi 

 Baird ; and less frequently so tar as I have observed, in Limncea 

 columella Say, L. caperata Say, and L. lanceata Gould. Doubtless 

 many others of the numerous alleged species of this genus, occasion- 

 ally exhibit this character of sculpture, which is seen in examples 

 of all of those I have named even from widely separated areas. 



It should not, however, be inferred that sculpture variation has 

 any special or direct relation or connection with geographical 

 distribution ; that it has indirectly, in the Limnceas and the class 

 of Mollusks to which said group belongs, there is no doubt, for it 

 will at once come to the mind of any one familiar with the pond 

 snails of all countries, that those inhabiting semitropical and tropical 

 areas are much more constant or uniform in size, shape and sculpture 

 than their fellows of the same kin from northern or colder latitudes, 

 and the texture of the former is much finer and smoother on the 

 whole, or all in all, than the forms that live in the cooler regions of 

 the north. The influences that appear to induce, or cause variation 



