86 THE NAUTILUS. 



A recent study of the eastern North American species has devel- 

 oped some unexpected peculiarities in regard to their surface sculp- 

 ture, which are of value in determining many of the species and 

 which may prove to be of importance in reference to their phylogeny 

 and classification. 



In studying the Ancyli, it is necessary to have the shells thor- 

 oughly cleaned with dilute oxalic acid and to use a compound micro- 

 scope of at least 50 diameters; not unfrequently a power of 100 diam- 

 eters is required, especially with the smaller species, to reveal the 

 characteristic sculpture. Under a simple lens of 10 diameters the 

 shell, when cleaned, appears to be smooth and shining, but under a 

 higher power a more or less developed system of sculpturing is vis- 

 able in n('arly every species. This consists of two elements : first 

 the concentric lines of growth, and second, a radial sculpture more 

 0/ less evident, which in its fullest development, as in A. peninsuJcp, 

 and eiigraptus, presents a series of fine, conspicuous, radial riblets 

 extending from the apex to the peritreme. 



The concentric sculpture formed by the growth lines is not usually 

 very strongly developed. It never presents the regular clear-cut 

 striation such, for instance, as is presented by Planorbis trivolrts, 

 but is irregular and more or less indented, varying in the different 

 species. 



Tiie radial sculpture in all the species examined, when present, 

 consists of fine transverse elevations varying from very fine, irregu- 

 lar, discontinuous ripples to continuous riblets covering the entire 

 surface. When present at all, their position is radial. 



The only species in which any other kind of radial sculpture has 

 been noticed is the A. borealis Morse, in which the surface is marked 

 " with fine, regularly interrupted radiating lines." It is not ex- 

 pressly stated that these are incised, but such would seem to be the 

 inference. Unfortunately no authentic specimens have been acces- 

 sible for examination. 



Tiiere is a large degree of individual variation in the development 

 of the radial sculpture, even in those sj)ecies which have been estab- 

 lished upon its presence and in which it is best developed. A. pen- 

 insuIcB is tlie only one in which it seems to be uniformly present. 

 A. filosus is frequently nearly smooth and, judging from specimens 

 from both the Coosa and the Cahawba, the radiating sculpture is 

 decidedly irregular. The same holds true in regard to A. eugraptus. 

 A. ova/is has not been examined. 



