ANIMALS. 195 



Diagnosis. — Slightly inequilateral : marginal outline somewhat oval transversely \ 

 umbones pointed : dorsal slope of each valve angulated : concentrically threaded.2 



The general outline of this interesting species is somewhat oval in the transverse 

 direction : its umbones are rather pointed ; and the surface of both valves is crowded 

 with sharp prominent striae. 



The specimen figured is a gutta-percha cast, of the natural size, taken from a 

 natural impression. Another impression of the same species, and from which a 

 number of similar casts might easily be taken, is in the London Geological Society's 

 collection, presented by the Rev. Professor Sedgwick. 



Whitley Quarry is the only locality known to me for Astarte Vallisneriana, where 

 it is extremely scarce ; though it would appear, that formerly specimens were more 

 abundant. (Vide Sedgwick, loc. cit.) 



Astarte Tunstallensis, King. Plate XVI, fig. 2. 



Diagnosis. — Nearly circular in its marginal outline : slightly inequilateral, the pos- 

 terior half being the widest, also the deepest : rather tumid at the umbones : 

 concentrically threaded : nearly a quarter of an inch in width. 



This species might be taken for the young of the former ; but it differs in having 

 the posterior half longitudinally deeper, compared with the anterior half ; the dorsal 

 margin less sloped ; and the umbones more tumid. It is similarly ornamented with 

 concentric striae. 



I have only found a single specimen, the one figured, of this species in the Shell- 

 limestone of Tunstall Hill. 



Family Pholadomyid^e, King, 1844. 



M. de Blainville's family Pglorida, and all the synonymous groups proposed by 

 other naturalists, are so heterogeneous, that I was induced some time since^ to propose 

 the present one for Pholadomga (the type), Panopcea, Lysianassa (Miinster), Cercomya 

 (Agassiz), and the following genus. 



The genera named are characterised with transversely oblong valves, an external 

 cartilage, a sinuated pallial line, and a slightly developed or extremely simple dental 

 system : judging from Pholadomya and Panopaa, the only recent genera known, 

 the cloak of the animal is entirely closed, with the exception of an anterior opening for 

 the passage of the foot, and an ingress and an egress orifice at the termination of a 

 long, posterior, siphonal sheath. 



1 In my Catalogue this species is incorrectly stated to have its "ventral outline semicircular." 



2 King, Catalogue, p. 11. 



3 Vide Annals and Magazine of Natural History, vol. xiv, p. 315. 



