138 BULLETINS" 111, UXITED STATES NATIOls^AL MUSEUM. 



1889. Cadulus gracilis, Dall, Bull. 37, U. S. Nat. Mus., p. 78 (not of Jeffreys, 1877). 

 1898. Cadulus gracilis, Pilsbry aad Sharp, Tryon's Man. Conch., vol. 17, p.lbo. 



in part. 

 1903. Cadulus gracilis, Dall, Bull. 37, U. S. Nat. Mus., p. 78 (not of Jeffreys, 187/). 



The shell is small, slender, slightly curved, little swollen, with its 

 section of maximum diameter about median. The cylinder is round 

 at the equator, but considerably flattened or compressed posteriorly. 

 The convex outline describes a fairly even arc, which is shghtly flat- 

 tened anteriorly. The concave outline shows a decided concavity 

 with a scarcelv perceptible convexity at the equator. The anterior 

 aperture is oblique, almost round, with its peristome rounded. The 

 apical orifice is flattened into an oval section and is relatively large 

 and a little flaring. There are one or more callous rings within it. 

 The apical characters are not positively determinable, but carry a sus- 

 picion of PlatyscMdes features. Measurements are: 



Length, 4.90 mm.; diameter, 1 mm.; anterior aperture, 0.55 mm.; 

 apical aperture, 0.5 by 0.4 mm. (Type.) 



Length, 4.75 mm.; diameter, 0.9 mm.-; anterior aperture, 0.5 mm.; 

 apical aperture, 0.5 by 0.4 mm. 



The type, Cat. No. 78238, U.S.N.M., was obtamed at the U. b. 

 B. F. Station 2682, off Nantucket, in 1,004 fathoms, bottom of green 

 mud and sand. 



This is the largest species of the series of Caduli compnsmg this 

 Vroup of very small slender forms. It is again characterized by the 

 very decided compression of the posterior fourth of the shell with the 

 resultmg oval apical orifice; also by the median equator, consistmg of 

 only a very slight expansion of the cylinder. Although Jeft'reys him- 

 self compared a specimen from the 843-fathom lot (station 2115) with 

 specimens of his own C. gracilis from British waters, and accepted 

 their specific identity, I feel it necessary to separate these Eastern and 

 Western Atlantic forms. The two species are undeniably closely re- 

 lated, belonging to the same group, but the English specimens are 

 smaller, more slender, and their apical orifices are not usually so de- 

 cidedly flattened. In the comparison of these very small Caduli one 

 senses certam differences that may result from some very slight cause, 

 as the degree of posterior curvature, or the degree of the anterior flat- 

 tening, or the angle of obliqueness of the aperture, or the exact relation 

 of maxmium diameter to the total length. These differences, if they 

 hold good throughout, seem sufficient grounds for separation of indi- 

 viduals taken from two sides of a great ocean, even though one may 

 not be able to set forth clearly in words these shell differences. 



