294 Mr. Hall on Microscopic Shells found in Marl Slate. 



rocks, and therefore it is a natural inference that these are full 

 grown. 



The following are clearly identified as specifically distinct, and 

 are all presumed to be new. 



Genus Mickoceras. Convolute, volutions few, horizontal, ra- 

 pidly diminishing from the aperture ; aperture subrhomboidal ; 

 shell subcarinated upon the back, chambered ? 



This fossil shell approaches to the genus Cyrtolites of Conrad ; 

 the whorls are contiguous but not involute, as in Bellerophon and 

 Goniatites. It is not easy to determine whether this fossil be 

 chambered or not. 



MicROCERAs inornatus. Yolutions about two, rapidly diminish- 

 ing ; spire equally depressed on either side, obtusely carinated or 

 angular upon the back ; carina more conspicuous near the mouth, 

 and gradually becoming obsolete ; aperture somewhat quadran- 

 gular ; surface smooth. 



Largest diameter -^\ of an inch. 



Genus Cyclora. Subglobose, shell thin, spire short, con- 

 sisting of a few whorls ; columella smooth, slightly reflected over 

 a minute umbilicus, aperture circular. 



N. B. The generic characters here given may be so extended 

 as to include several shells of the palaeozoic strata which cannot 

 properly be included under existing genera. 



Cyclora minuta. Smooth ; volutions about three, rapidly ex- 

 panding towards the mouth ; spire moderately elevated ; aperture 

 round and well defined. The last whorl forms the principal part 

 of the shell. 



Height of shell ^V to sV <^f ^n inch. 



This species is exceedingly numerous among those obtained by 

 Mr. Carly, there being twice as many of this one as of all the 

 others. 



Turbo? parvulus, n. s. Spire elevated, volutions about four, 

 smooth ; first whorl angulated upon the centre towards the aper- 

 ture ; outer edge of the aperture projecting downwards. 



Height of shell y'j of an inch. 



NucuLA ohliqua, n. s. Subquadrangular ; hinge-line short, ob- 

 lique ; beaks very prominent ; edges of the shell thin ; anterior 

 side abruptly rounded, posterior slope abrupt. 



Length and breadth about equal, ^^ of an inch. 



