268 



loped in the tertiaries, while from the present seas not 

 less than 200 species have been obtained." 



It is much more difficult to reconcile the synonymy 

 of our native species than to distinguish them. As Loven 

 has justly remarked, t{ Cardia europaea misere confusa." 

 I will endeavour not to increase this perplexity, with- 

 out disregarding, however, the established rules of pri- 

 ority and general usage. 



The meaning of the generic name (heart-shaped) 

 will appear when the united valves are viewed in profile. 

 The genus Cerastes was formed by Poli for the animal. 



A. Shell more or less globular ; ribs strong, and covered with 

 spines, tubercles, or vaulted scales. 



This section may be further subdivided into 



a. Round. 1. C. aculeatum. 2. C. echinatum. 3. C. tu- 



berculatum. 4. G. papillosum. 



b. Triangular. 5. C. exiyuum. 6. C. fasciatum. 7. C. 



nodosum. 8. C. edule. 



c. Longitudinally oval. 9. C. minimum. 



w. 3^. 1. CARDIUM ACULEA'TUM *, Linne. fttt j 



C. aculeatum, Linn. Syst. Nat. p. 1 122 ; P. & H. ii. p. 4, pi. TYTJIJ. f. 1. 



BODY of a vermilion colour : foot long and awl-shaped. 



SHELL very gibbous, with a somewhat oblique outline, thin 

 for its size, opaque and rather glossy : sculpture, 20-22 strong 

 compressed ribs, which are a little broader than the furrows 

 between them ; each rib is divided in the middle by a ridge of 

 spines, which bend towards the posterior side, being longer and 

 double on that part and tubercular on the anterior side ; the 

 furrows are transversely striated, or in aged specimens are 

 marked with flexuous wrinkles ; in younger shells there are a 

 few irregular longitudinal lines, giving the furrows an appear - 



* Thorny. 



