Tate — List of Irish Liassic Fossils. 15 



the centre whorls the ribs are distinct, numerous, close, sharp and having only 

 a slight sigmoidal bend. The species is peculiar to the Irish Lias. 



3. Cerithium tenuicostatum, Portlock sp., Plate I. fig. 8. 



Turritella ( Cerithium) tenuicostata, Portlock, Geol. of Deny, p. 124(1843). 



This species was described by Poitlock, in the following words : — "Whorls 

 convex ; spiral threads of two sizes ; three strong on the lower half of the whorl, 

 and one fine below them. On the upper half there are four or five fine threads, 

 which are very close together ; whilst the strong threads of the lower half are sepa- 

 rated by a considerable space. The fine threads are in like manner separated 

 from the strong, by a space equal to the separating space of these lines. All 

 these spiral threads are crenulated by numerous very fine-curved longitudinal 

 threads, of which there must be more than 30 on a whorl. Very minute, 6 

 whorls in '25 of an inch." 



C. tenuicostatum is a very variable species ; when the medial longitudinal 

 ribs are prominent, the whorls are bicarinated, as shown in fig 8, (*) which re- 

 presents an extreme form; whilst on the other hand, as the threads assume less 

 prominence, the whorls become proportionately more regularly convex. It 

 agrees in all its characters, except that of size, with C. Semele, D'Orb., with 

 which it is associated, and should further examination prove that C. tenui- 

 costatum is only a depauperated condition of C. Semele, then Portlock's name 

 has priority of publication. 



4. Cerithium percinctum, Portlock ( Turritella), loc. cit, p. 123. 



" Very minute, eight whorls in "25 of an inch. Of the raised spiral lines, one 

 along the centre of the whorl is more elevated than the others, and another 

 below is nearly as much so — a finer line being between; which produces the 

 appearance of a band. Above the stronger line there are three or four finer, 

 though still well-marked lines; and below it also three or four, including the 

 second stronger line." 



I have not met with any shell that agrees with the above description, and 

 the type appears to have been lost. But that no mention is made of transverse 

 striae, and indeed it must be conceded that none are present, because com- 

 pared by Portlock, with T. minuta, K. & D. , and T. cingenda, Sow. , in which 

 no transverse striae occur, I should be disposed to regard this species as the 

 bicarinated form of C. tenuicostatum. 



5. Chemnitzia punctata, nov. spec, Plate I. fig. 11. 



Shell conical, whorls about six, sub-inflated, with numerous narrow de- 

 pressed longitudinal costatulae, with about equally broad slightly impressed 

 sulci, which are regularly pitted ; the punctuations are ranked transversely by 



* The transverse ribs are much finer and more numerous than shown in the figure ; and 

 the whorls should have been more markedly bicarinated. (r. t.) 



