34 Mr. R. Etheridge on Carboniferous Mollusca. 



the apices of the angles in each range, anterior and posterior, 

 turned towards the cartilage-pit or umbo. The cartilage-pit 

 is pyriform and oblique, its smaller or pointed extremity being 

 placed immediately under the apex of the umbo, then expand- 

 ing somewhat outwards and downwards into the cavity of the 

 valve. 



Dr. F. Roemer has given a figure of the interior of N. gib- 

 bosa, in the lately issued plates* of his ' Letheea Geognostica ;' 

 but I do not observe any trace of a cartilage-pit there repre- 

 sented. The specimen must have been faulty or of another 

 species. 



With regard to Nuculana {Lecla) attenuata^ Flem,, the case 

 is somewhat different ; for, so far as I am aware, the hinge- 

 structure of this species has never been minutely described, al- 

 though it may have been referred to in general terms by several 

 authors. The hinge (figs. 6 & 7) is similar to that of N. gibbosa^ 

 with its anterior and posterior teeth well developed. The teeth 

 and sockets increase in size outwards from the cartilage-pit, 

 which occupies the apex of the arch. The number of the 

 teeth is considerable in N. attenuata : in one specimen I 

 have counted twenty-three on the longer side of the shell ; and 

 even then the series was incomplete. In the left valve the 

 teeth are produced inwards [t. e. towards the beak) and out- 

 wards (/. e. into the cavity of the shell) into projecting den- 

 ticles ; so that the interlocking of the two series must have been 

 very complete and secure. I wish more particularly, how- 

 ever, to draw attention to the cartilage-pit (a, figs. 6 & 7), which 

 is triangular with a rounded base, and inclined, in most speci- 

 mens 1 have examined, a little obliquely towards the shorter 

 side of the shell. Prof. M'Coy notices the teeth of this shell 

 in his description of it ; but he appears to have been unable to 

 satisfy himself as to the presence of a cartilage-pit f. 

 Collector — Mr. J. Bennie. 



EXPLANATION OF PLATE I. 



Fig. 1. EntoKum demissum, Pbillips, showing hinge-structure, after 



Quenstedt (Der Jura, Atlas, t. 48. f. 6). 

 Fig. 2. Entolimn aviculaticm, Swallow, valve with the elevated ears, 



after Meek (Hayden's Final Geol. Report on Nebraska, 1872, 



t. 9. f. 11,/). 

 Fig. 3. The same, opposite valve to fig. 2 (loc. cit. f. 11, g). 

 Fig. 4. Entolium Sowerbii, M'Coj^, valve with elevated ears ; natural 



size. 

 Fig, 5. The same, opposite valve to fig. 4. The same letters refer to cor- 



• 1. Theil, 1876, t. 44.f. 13, c. 

 t Brit. Pal. Foss. p. 512. 



