114 PROCEEDINGS OP THE ACADEMY OF 



inclined to think it belongs to that group. It has exactly the 

 form, size, surface, aperture, and lip, and even the irregularit}', of 

 the embryonic volutions seen in AcicuUna; while the only differ- 

 ence I have been able to see is, that its embryonic turns, instead 

 of forming a minute cone turned to one side at right angles to 

 the longitudinal axis of the body of the shell, have the form of 

 a Plaiiorbis standing edge upward. Whether or not this slight 

 peculiarity in the minute apex ma}' have been accompanied by 

 some important difference in the structure of the animal, it is of 

 course impossible to sa3^ 



The specific name is given in honor of R. P. Whitfield, Esq., of 

 Albany, New York. 



Locality and position. Danville, Illinois, where it occurs with 

 many other small shells of the Coal-measures, in a bed of shale 

 immediately over the coal-mine of that place. 



LOXONEMA ATTENUATA, var. SEMICOSTATA. 



Chemnitzia attenuata, Stevens, 185S, Am. Journ. Sci., vol. xxv. (Sec. 

 series), p. 259. — (Not Loxonenia attenuata, Hall, 1859.) 



Shell very small, elongate-conical, somewhat more tapering 

 above than below the middle ; volutions about twelve, slightly 

 convex and increasing gradually' in size from the apex, the last 

 one being rounded and not larger in proportion to the regular 

 increase of the whole than the others ; suture distinct ; aperture 

 ovafe, scarcely equalling one-fourth the entire length of the shell. 

 Surface of the upper volutions (excepting one or two of the smooth 

 apical turns) each ornamented by thirteen or fourteen very regu- 

 lar, straight vertical costse, about equal in length to the furrows 

 between ; farther down these costfe gradually become obsolete, so 

 that tliree or four of the lower volutions show only minute lines 

 of growth that are invisible without the aid of a magnifier. 



Length of a rather small specimen, 0.13 inch; breadth, 0.15 

 inch; slopes of spire slightly convex and diverging from the apex 

 at an angle of about 18°. 



This little shell is evidently closely allied to the form called 

 Chemnitzia attenuata by Dr. Stevens, but its volutions increase 

 more rapidl}', and have the costse smaller. It is probablj' a dis- 

 tinct species, but until more specimens can be examined with the 

 view of determining how far the species varies in the characters 

 mentioned, I have preferred to place it as a variety L. attenuata. 



[August 15, 



