'TURRITELLA. 



thict^ but an attentive examination of tlie striae of growtti 

 will always prove its existence; the lower part of the 

 outer lip becomes more prominent in proportion as this 

 sinus is deep. Besides the above-mentioned sinus, there 

 is also a more or less distinct canal at the lower and inner 

 part of the lip, this canal is not reflected, but the lip is 

 here turned a little outwards, though not backwards; this, 

 Lamarck, does not, indeed, seem to have observed, 

 cepting in some fossil species, although in his T. exoleta 

 it is very strongly marked; in all it is more distinct than 

 in Scalaria. This, as well as the sinus in the outer lip, is 

 not so easily observable in our common English species, 

 which we call Turbo Terebra, as in most others; but it is 

 to be remarked, that we do not commonly meet with this 

 shell in a perfect state. Tlie species of Turritella, are not 

 usually umbilicate ; indeed, we know but of one species, 

 the T, perforata, Lam. that is so. 



Of recent species, we believe, there are a considerable 

 number; but they are difficult to distinguish from each 

 other, on account of the variability of the ridges and 

 striae on the outside. The fossil species are also numerous, 

 they are found in considerable numbers in the Green Sand, 

 London Clay, and in most of the newer beds : as at Grig- 

 iion, Bordeaux, Barton, and most other places where these 

 beds occur. 



Fig. 1. Turritella dicplicaia, a common species, the Turbo dnplicatus. Linn. 

 hut exceedingly variable in its ridges ; this is generally admitted in the catalogues 

 Of British shells, but as we apprehended without sufficient reason. 



2. Turritella sulcata, Lam. a fossil species from near Paris. 



3. exoleta, Lam. remarkable for the concavity of the center of 



its volutions. 



4. Turritella sinupsa, testa turrita, costis transversis obtusis ; sinu labii 

 externi magno, basique emarginat^. 



Obs. — An hitherto un described fossil species from 

 Bordeaux, where it is found with many other shells in a 

 kind of yellow sand, the form of its aperture is rather 

 peculiar. 



5. Operculum of the common English Turritella, which we commonly 

 call Turbo Terebra ; it does not agree with Laiiiarek's Turritella Terebra; but 

 more nearly resembles his T. (sornca. 



