found on the coast of Northumberland and of Durham. 241 



Moller under the name of Yoldia for those Nuculas which agree 

 with the last in being furnished with siphons, but which are 

 thin, gaping, and of an oval form. Prom Yoldia we pass with little 

 difficulty into Solenella — a genus whose affinities appear never to 

 have been properly understood : the principal difference between 

 Solenella and Yoldia is in the situation of the cartilage, which in 

 the former is external, while it is internal in the latter ; but this 

 difference does not constitute any serious objection to an intimate 

 relationship existing between these genera, since the like differ- 

 ence occurs even in closely related species of the same genus ; for 

 example, Lmcina divaricata has an external cartilage, while L. un~ 

 dularia*, Wood, has one that is decidedly internal. 



There can be little or no doubt that Nucula and Leda are closely 

 related to each other ; hence we have another case, besides the 

 one founded on the relation of Iridina to Anodonta, as first 

 pointed out by Deshayes, u considerably invalidating the esta- 

 blished rule t" that would compel us to include in one great fa- 

 mily, the Inclusa of Cuvier, all those shells with " the mantle open 

 at the anterior extremity, or near the middle, for the passage of 

 the foot and extending to the other end in the form of a double 

 tube/'' To carry out such a rule would be to group together the 

 most heterogeneous forms, and to widely separate those inti- 

 mately related to each other by affinity : the genera Unio, Ano- 

 donta and Margaritana } which have the mantle open from front 

 to back, ought in such a case to be placed Hear the Monomyarians, 

 while Iridina and Columba (Leila, Gray ?), Lea, which have all 

 the characters, at least the last genus, of the Enfermes, ought to 

 be collocated with the Solens, Myas and Panopseas. 



Astarte scotica, Montagu. 



This species is somewhat rare on our coasts, where it occurs in 

 deep water. The principal character which distinguishes it from 

 Astarte damnonia? is the plainness of the margins : I have a spe- . 

 cimen however with the basal margins plain, but whose posterior 

 and anterior margins are crenulated. Generally the inside of the 

 valves, as well as the animal, are light-coloured, but occasionally 

 they are red ; it is the same with Astarte damnonice. 



* Mr. Searles V. Wood places this interesting shell in the genus Loripes 

 (vide Annals of Nat. Hist. vol. vi. p. 247), but its resemblance to Lucina 

 divaricata plainly shows, that if this were agreed to, we should break one of 

 the most obvious links of affinity, and group together shells not so closely 

 related. The change of position of the cartilage is, I am inclined to think, 

 to be seen in other closely allied species of Lucina ; if so, the genus Lorijpes 

 would be far from a natural one. 



t Animaux sans Vertebres, 2nd ed. tome vi. p. 572, &c. 



