BIVALVIA. 73 



form, as well as possessing a linear series of denticles, seem to point out its place 

 as near to Nucula from which it differs essentially, in having an external ligament, 

 and one large lateral tooth upon the anterior side. 



The shell is of a nacreous texture within, and was, probably, covered with an 

 epidermis in the recent state. The ligament is placed on the posterior side of the 

 umbo, upon a small projecting portion of the shell, and the animal was without 

 prolonged siphonal tubes, the line impressed by the edge of the mantle being like 

 that of Nucula, without any indentation. There are no recent species, that I am 

 acquainted with, possessing such a dental arrangement, and its true position is of 

 course conjectural. The linear teeth and external ligament resemble Pectunculus, with 

 a form like that of Nucula. 



1. NUCINELLA MILIARIS, Deshayes* Tab. X, fig. 4, a c. 



NUCULA MILIARIS. Desk. Coq. Foss. des Env. de Par., torn, i, p. 225, pi. 36, figs. 7-9, 



1829. 

 PLEURODON OVALTS. 5. Wood. Illust. in Mag. Nat. Hist., 2d Series, vol. iv, p. 231, pi. 13, 



fig. 1, 1840. 

 MILIARIS. S. Wood. Catalogue, 1840. 



Spec. Char. Testa minima, sulovatd, l&vigatd, politd, tumidd ; postice subtruncatd, 

 antice productiore, rotundato-ovatd : dentibus 5 6 magnis, (Musis. 



Shell minute, subovate, smooth, glossy, and tumid ; posterior side short, subtrun- 

 cate, anterior large, roundedly ovate ; teeth 5 6, large and obtuse. 



Diameter, T ^- of an inch. 



Locality. Paris Basin, Grignon. 



Cor. Crag, Ramsholt, and Sutton. 



This pretty little shell is by no means rare at either of the above British localities, 

 and at the former (Ramsholt), the valves are often found- united, the large and pro- 

 minent teeth with which they are furnished having kept them in their natural position. 



It is one of the very few of our Crag Molluscs, that dates its existence from the 

 Older Tertiaries, or what is called the Eocene Period ; as there is reason to believe 

 the species left in the Paris Basin is the true progenitor of our little shell, while it 

 appears to have died out before the severer conditions of the Red Crag Period had set 

 in : although so small a shell, it would not readily be found, unless abundant, in a 

 deposit so disturbed. 



As, however, some differences exist between the Crag Fossil, and what is here 

 considered its specific parent, it may be necessary to give a more detailed description 

 and to point out what, perhaps, might be regarded by some Conchologists as of 

 sufficient importance to keep them distinct. 



Our little shell in its outward form, slightly resembles a minute specimen of 

 Nucula nucleus, except, that it is more tumid ; the anterior side constitutes nearly 

 the whole of the shell, the posterior being cut off by an almost straight line from the 



10 



