190 J. S. GABDKEE ON BRITISH CRETACEOUS PATELLIDiE ETC. 



FISSURE LLID^E. 



Emarginula neocomiensis, D'Orb. Neocomian. PI. VIII. figs. 1-6. 



Shell oblong, twice as long as high, solid, conical, convex ante- 

 riorly, slightly concave posteriorly ; apex small, recurved, about § 

 posterior ; sculpture, 26 to 30 strong narrow principal ribs, and the 

 same number of intermediate ribs, the last varying in prominence 

 in different specimens, and not appearing at all until the shell is 

 well advanced in growth ; the ribs are cancellated in full-grown 

 specimens by 25 to 30 elevated lines of growth, which pass over the 

 secondary, but not over the principal ribs (fig. 6a). In two very 

 perfect specimens in the Leckenby collection, Woodwardian Museum, 

 there is a node at every intersection (figs. 1, 2, 2 a). The slit is 

 short, and placed rather to the right of the median line. D'Orbigny's 

 figure in the ' Pal. Prang.' has this character rather exaggerated ; and 

 it usually occupies a more symmetrical position. Pictet and Cain- 

 piche had five examples under examination, in all of which the fissure 

 deviated. Amongst the number of specimens which I have exa- 

 mined, the fissure, I find, usually deviates ; but the character is not 

 constant. The slit is bordered on each side by a principal rib ; the 

 scar forms, between two of the principal ribs, a narrower region than 

 the space occupied by an intermediate rib, and is imbricated trans- 

 versely. There is no trace of spiral growth in any of the specimens. 

 The cast is smooth, except at the margins, where it bears impres- 

 sions of all the ribs. The line of fissure presents a broad furrow, ex- 

 tending from near the apex to the margin, in the centre of which is 

 a slightly raised region terminating at the fissure (PI. VIII. fig. 2). 



Although very distinctly characterized, it has been confounded 

 with E. Guerangeri, D'Orb., of the Chloritic Marl, from which it is 

 readily distinguished by its greater number of ribs. 



Pictet and Campiche, 'Terr. Cret. de Ste. -Croix,' mention a va- 

 riety which has the primary and secondary ribs equally prominent ; 

 there is a similar example in the Woodwardian Museum, from Don- 

 nington, Lincolnshire, which has about 54 ribs and a median 

 fissure, and may prove distinct when more specimens are available. 



There is apparently no specific difference between the specimen 

 from the Atherfield clay, and one from Speeton, in the Jermyn-street 

 Museum, named E.Jlssaria, Forbes. 



The largest specimen I have seen is from Seend, and is in the 

 British Museum (figs. 3, 4), measuring 1. 2b millims., b. 18 mil- 

 lims., ht. 13 millims., these dimensions being considerably in ex- 

 cess of those usually met with. 



E. neocomiensis, D'Orb., was first described as E. reticulata by 

 Leymerie, in 1842, and was figured the next year by D'Orbigny in 

 the ' Pal. Franc. Terr. Cret.' vol. ii. p. 392, pi. 234. figs. 4-8, and 

 again by Pictet and Campeche, ' Terr. Cret. de Ste.-Croix,' pi. 

 xcvii. figs. 9-11. 



The species is very generally distributed throughout the Lower 

 Green sand, which it characterizes, and has, no doubt, as wide a 



