290 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxiv. 
a first serios, which exhibited the extremes and other aspects of varia- 
tion more markedly, having unfortunately been misplaced/ 
A fair idea of the size as a whole is not given by the plate, the 
examples selected being- simply to illustrate variation; they are con- 
sideral)!}^ under the average. 
SCULPTURE AND SALINITY. 
The presence of sculptural characters in the Phys/dce is of rather 
rare occurrence, though frequently met with in many species of the 
Linmiplclw, which sometimes exhibit much diversit}- within quite 
limited geographical areas. While the Paludestrina? of the desert are 
so conspicuous in prominence and diversity of sculpture, the Physas, 
on the contrary, show only the usual incremental lines more or less 
defined. The following species of Physa^ as described by various 
authors,' are said to be sculptured: P. costata Newcomb, from Clear 
Lake, California;'' P. lord! Baird, Lake Osoyos, British Columbia; 
P. innom Gould, Lake Superior; P. pllcata De Kay, Manhattan 
Island; P. sol! da Philippi, New Orleans. 
In all of the foregoing, excepting Dr. Newcomb's P. costata, the 
sculpture consists either of fine lir^e or indented grooving, which 
crosses the incremental strite or lines of growth. This is what I 
have called tran.werse sculpture. 
The elevation of Clear Lake is 1,350 feet, with an area of 80 square 
miles. It is subject to only slight fluctuations in volume. 
The incremental strife, though sometimes quite conspicuous, are 
ordinarily exceedingl}^ fine or nearh^ obscure. They^ can onh' be 
regarded as sculpture in a negative sense. These are, of course, longi- 
tudinal, being parallel to the axis of the shell, or nearly so. In some 
instances "'fine broken microscopic wrinkles parallel to the lines of 
growth occur,"' as mentioned l)v Philippi in his description of P. 
HK^i'lcana. P. idiUlppii Kiister is described as having "waving 
wrinkles." 
Where these forms of sculpture are present the result is seen in a 
more or less finely decussated or reticulated surface, which may extend 
over a part or cover the entire surface of the shell, the latter rarely. 
Dr. Newcomb's Phym. costata is the only species which exhibits 
really conspicuous longitudinal sculpture. In this regard it is a 
remarkable exception to all others of the Physida'. It is a very pretty 
^ See Plate xxiv. 
'"'See Binney's Land and Fresh Water Shells of North America, Part II, Smithsonian 
Miscellaneous Collections, p. 143. 
*Dr. Cooper, who collected some fifteen species of moUusks in Clear Lake, says: 
The borax, soda, alum, iron, sulphur, etc., found around the lake, do not affect the 
taste of the water, and do not seem to influence animal life except in limited spots 
where no mollusca are found, perhaps on account of subaqueous mineral springs. 
Proc. Cal. Acad. Science, IV, p. 154. 
