78 MOLLUSCA FROM THE CRAG. 



fossil, but I think distinct from the Paris basin shell, P. terebettata, Desh. (Coq. foss. 

 des Env. de Paris, pi. 22, f. 7-8.) In the Crag shell, the upper fold upon the columella 

 is large, sharp, and elevated, with very little obliquity ; below it are two small oblique 

 folds, nearly equal sized, the lower one forming the base of the columella, and producing 

 there an incipient sinus ; the outer lip is sharp, and it has about half a dozen obtuse 

 teeth within it, which are not continuous, but produced at intervals. 



It is nevertheless possible that this may be the same as the Eocene species, but 

 my specimens are all so much less, as well as differing in other characters, that I have 

 left it with my provisional name until more accurate comparisons can be made with 

 the foreign shell. 



CHEMNITZIA,* D'Ord. 1839. 



TURBO (spec.) Mont. 



TURBONILLA. Leach, 1819. 



PARTHENIA. Lowe, 1842. 



ORTHOSTELIS. Arad. and Magg. (ex Phil.} 



PYRGISCUS. Philippi. 



EULIMA (spec.) Philippi. 



LOXONEMA (?). Phillips. 



MELANIA. Scacchi. 



EULIMELLA. Forbes. 



Gen. Char. Shell turriculate, with numerous volutions, nearly flat, having a distinct 

 suture, aperture subquadrate, columella straight, with or without a fold ; apex mam- 

 millated by the reversed position of the extreme spire, exterior generally striated or 

 costated, sometimes smooth and plain. 



Dr. Leach, in MS., united a group of shells with these characters, to which he 

 gave the name of Turbonilla, which was adopted by Risso in 1826. In June, 1840, 

 the Rev. T. Lowe read a paper before the Zoological Society, describing several of 

 these species, and proposed for them the generic name of Parthenia, considering that 

 given by Dr. Leach as being incorrect in composition, and otherwise preoccupied by 

 another genus of Mollusca. In 1840, according to M. Philippi, Wiegman proposed the 

 name of Pyrgiscus for some marine Melaniae, which it is probable was intended for 

 these shells. In 1839, M. d'Orbigny published some species under the above name 

 (in Webb and Berth. Hist. Nat. des lies Canar. Moll.), and this name appears to have 

 the precedence of all but that of Leach. M. Loven, in his Synopsis, has restored the 

 name of Turbonilla, which perhaps, after all, notwithstanding the objection by 

 Mr. Lowe, ought to be the one employed. 



In the young state, probably before its exclusion from the egg, the first volution 

 appears to have taken a sinistral form, and afterwards to have changed into a dextral 

 direction, and the apex is rendered obtuse by the folding down or horizontal position 

 of its primary volution. 



* Etym. After Chemnitz. 



