Mat 30, 1919] 



SCIENCE 



521 



United States, but especially common in the 

 west and southwest, in the more arid parts of 

 the country, where water stands for but a 

 small part of the year and where the lymnseas, 

 and other mollusks must be able to withstand 

 the period of drouth by hibernating in cracks 

 in the bottom of the pond or stream. Such 

 species as Galha caperata (Say), 0. cubensis 

 (Pfr.), and 0. buUmoides and its varieties are 

 typical of these habitats. Galba palustris and 

 some other species normally living in marshes 

 may at times be compelled to adopt this hiber- 

 nating type of habitat during unusual i)eriod3 

 of drought. 



The writer has not found lymnseas as a rule 

 inhabiting moss, although the little amphib- 

 ious species (parva, dalli, etc.) may do so in 

 some places and have, indeed, been collected 

 from such a habitat. All Ijinnseas as well as 

 other fresh water mollusks, whether in lake 

 or marsh habitats, prefer a location where 

 there is a quantity of vegetation and where 

 there is an abimdance of filamentous alges 

 (Cladophora, (Edogonium, etc.) upon which 

 they largely feed, in some cases to such an ex- 

 tent as to give a green color to the shell. 

 The relation of algse to molluscan and other 

 life has recently been rather fully stated by 

 the writer.' 



It is interesting to note that fresh-water 

 mollusks, the lymnseas in particular, respond 

 quickly to changes in environment, a species 

 characteristic of a marsh adapting itself to a 

 rough lake shore habitat if compelled to make 

 the change. Thus typical stagnalis is char- 

 acteristic of quiet, pond-like bodies of water, 

 while the variety lilliancB lives on a shore ex- 

 posed to the full force of the waves. The 

 change in habitat has resulted in a larger 

 aperture and foot in lilliance the better to 

 resist the moving power of the waves. In 

 Oneida Lake, a large colony of Galha palustrU 

 was forced by a change in the environment, 

 caused by the barge canal construction, to 

 change from a shallow swampy habitat to that 

 of an open rocky shore exposed to violent wave 



7 Tech. Pub., No. 9, N. Y. State CoHege of For- 

 estry, Syracuse University, 1918. 



action. The effect of this change has been to 

 produce a shell with a wide, flaring aperture 

 and a larger foot area, a direct response to the 

 environment which demands a larger foot area 

 for resisting the waves.' The lymnseas are 

 not, as generally supposed, mollusks chiefly of 

 ponds and ditches, as might be thought from 

 reading the paper in Science, but also of the 

 larger inland lakes, in fact a greater variety 

 is found in the lakes than in any other kind 

 of habitat. 



The fossil lymnseas, as well as other fresh- 

 water fossil groups, are in need of careful re- 

 vision in the light of modern work on the ex- 

 isting species. As the shell in a measure 

 reflects the internal structure, this revision 

 ought not to be difficult with ample mate- 

 rial of fairly well-preserved specimens. The 

 twenty-five or more species described appear 

 to represent the larger groups recognized 

 among the recent forms. Several of these 

 species, as mentioned by Hannibal, are prob- 

 lematic and may belong to other groups, but 

 more perfect material is needed for this pur- 

 pose. Some confusion of species has occurred 

 in figuring and describing a few of these 

 lymnseas, attention to which has already been 

 directed by the writer.' 



Frank Collins Baker 



Univeesity op Illinois 



SPECIAL ARTICLES 



SOUND AND FLASH RANGING' 



The location, by means of sound, of active 

 enemy batteries and the direction of the fire of 

 the friendly artillery on these and other enemy 

 objectives is new; has been successfully prac- 

 tised by the Allies and has been clumsily prac- 

 tised by the Germans. The location and rang- 

 ing by visual observation (flash ranging) is an 

 outgrowth of standard artillery methods and 

 differs from these chiefly in the extent of front 

 covered by a single group of observers and by 

 the adoption of certain electrical devices and 



• Baker, Tech. Pub. No. 9, N. T. State College 

 of Forestry, p. 180. 



» ' ' Men. Lymn. N. Am., ' ' pp. 89, 95, 96. 



» Abstract of paper presented before the Ameri- 

 can Philosophical Society, April 26, 1919. 



