78 MOLLUSCA FROM THE CRAG. 



fossil, but I think distinct from the Paris basin shell, P. terebellata, 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' Orb. 18S9. 

 Turbo (spec.) Mont. 

 Turbonilla. Leach, 1819. 

 Parthenia. Lowe, 18-12. 

 Ortiiostelis. Arad. and Magg. (ex Phil.) 

 Pyrgtscus. 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 mammillated 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. 



* Etvm. After Chemnitz. 



