NO. 2.] SNAILS OF THE GENUS 10— ADAMS. 9 



An animal as characteristic of such definite environmental conditions may be expected 

 to show equally marked characteristics which permit it to live in them. This is conspicuously 

 shown in the great muscular strength of the foot. Many years ago Miss Annie E. Law, of 

 Concord, Tenn., observed that (Lewis, '71, p. 223), "The muscular power of lo is astonishing. 

 I frequently find one adhering to a rock half as large as my head, and when I take up the shell 

 it brings the rock with it, and requires much force to separate it." These observations were 

 in aU probabihty made in the Tennessee River between Little River Shoals, below KnoxviUe, 

 andtheChota Shoals, about 20 miles below. (Lewis, 1. c, p. 216). This strength, therefore, 

 applies to the large individuals of loudononsis or turrita, and not to the smaller forms, although 

 they are also well able to maintain a hold in swiftly flowing water. An orienting response to 

 the swift current might be expected, but this subject has not been carefully investigated. 

 Wetherby ('76, p. 5) remarks that in the PoweU River at Kraushorns Ferry: "The los lay thick, 

 cHnging to the rocks, generally across the current." My own observations were neither detailed 

 nor definite enough to recognize a rheotropic response. 



The food of lo consists of the slimy algal coating and entangled organic debris on the rocks, 

 bowlders, and gravel upon which they creep. Wetherby ('76, p. 3) speaks of the food habits 

 of the family as follows : 



The Strepomatidae feed upon the confervae growing upon the rocks and stones in the river, through which the 

 tortuous path they eat in their meal takings may easily be seen. Now, every flood of a mountain stream, with its 

 rasping sand and gravel, has a tendency to scour off this growth, and to subject the animals that feed upon it to a 

 greater or less privation in regard to food. 



A series of lo Jluvialis from Cliuch River (lot 53) which I kept in a glass-sided aquarium 

 were seen to feed upon the algae growing upon the well-lighted side of the vessel. This may 

 explain, in part, their apparent preference for the sides rather than the bottom of the vessel. 



The large quantities of lime used in the formation of the shell must thus be secured from 

 this algal slime. A study of the conditions which determine the growth of these algge will 

 undoubtedly throw much light upon the occurrence of these shells. The absence of lo from 

 certain streams may be due in part to the dependence of certain algse upon lime, which is largely 

 lacking. It is weU known (Davis, '01, p. 495) that certain algse secrete and concentrate Hme 

 from fresh waters as well as that some perforate the living shells of moUusks. (Cf. Collins, 

 Erythea, vol. 5, p. 95, 1897.) Upon the shoals in the smaller rivers lo was very commonly 

 associated with Anculosa, so that it is probable that the two are competitors for food. Mr. 

 HinMey found a single specimen of lo tufrita on the Muscle Shoals of Alabama associated with 

 Angitrema and Anculosa. 



The reproductive habits of lo have an important bearing upon the interpretation of the 

 peculiarities of this group but little attention has been given to this subject. In this famUy 

 Stimpson ('64, p. 45) has shown that the sexes are distinct and that there is an absence of a 

 copulatory organ in the male. The external character, by means of which the sexes may be 

 distinguished, is by the presence, in females containing ova, of a "conspicuous slit or sinus in 

 the right side of the foot, about midway between the tentacle and operculigerous lobe" and the 

 absence of this sinus in the males. Stimpson (p. 46) further remarks: 



In view of these remarkable characters of the sexual system, the Melanians, the American species, at least, must 

 be separated from the ordinary Ctenobranchiate Gasteropods as a group of far more than family importance; for by 

 the entire absence of an intromittant organ in the male, which must be connected with a very peculiar, and as yet 

 unknown, method of impregnation, they diverge greatly from other families of the group, and approach the Cyclobian- 

 chiata. * * * There is no difficulty in conceiving that the impregnation may take place in the way which is known 

 to occur in the Lamellibrianchiata, the spermatic particles reaching the ovary of the female through the medium of 

 the water, into which they are discharged by the male. In our freely-moving Melanians, however, such a mode of 

 impregnation is quite unnecessary; it is far more probable that some direct connection takes place between the sexes; 

 and it is highly desirable that this subject should be carefully investigated, at the proper season, by those who have 

 the opportunity of doing so. 



Haldeman ('41, p. 22) states that this family is oviparous, a fact confirmed by Stimpson 

 ('64, p. 46). 



