122 



one. The species may be grouped under at least a dozen different sections. 

 In the type represented by the large L. tigerina and exasperata, including 

 L. punctata (Codakia, Scopoli), the shell is strongly radiately furrowed or 

 sculptured with scaly decussating ridges, and the inner margin is mostly 

 stained with a deep rose-pink ; in L. Jamaicensis (Phacoides, De Blain- 

 ville) the shell is only sculptured concentrically, and a curious allied type 

 is presented in L. Pennsylvania, in which the shell is invested with a 

 brittle transparent horny epidermis, that turns back from the ridges in 

 particles, which become solidified like little hailstones ; in the remarkable 

 L. Childreni (Miltha, Adams) one valve is flat and smaller than the other ; 

 in L. gibba and divaricata and a few others (Shigella, Turton), the shell 

 is sculptured with obliquely waved divaricating lines ; in L. leucoma (Lo- 

 ripes, Turton) the ligament has an unusually deep-seated position ; L. 

 spinifera (Myrlea, Turton) partakes rather of the character of Artemis in 

 respect of sculpture; L. borealis (Triodonta, Schumacher) is a solid densely 

 striated shell, and L. rotundata (D/plodouta, Brown) is characterized by 

 an erect bifid tooth ; while in L. Philippinarum, whose habit is to bury in 

 sandy mud at the roots of Mango-trees, we have a type more distinct than 

 all, in which the shell is thin, almost toothless, and the hinge is strength- 

 ened in the absence of teeth by a different position of the ligament, which 

 forms a broad strap, as it were, across the dorsal margins of the valves.* 



A feature not to be overlooked in the shell of Lucina is the position of 

 the lunule, which bears more on one valve than the other; the shell, in- 

 stead of opening, as in Artemis, through the centre of the lunule, opens, 

 in most species, on one side of it. The Lucina are variously distributed 

 in the European, Eastern, Australian, and Central American Seas, seven 

 species (including JJiplodonta) being inhabitants of our own shores. 



1. Anatellinoides, Reeve. 



2. annulata, id. 



3. Antiilarum, id. 



4. arcuata, Mont. 



5. argentea, Reeve. 



6. aurantia, Desk. 



7. barbata, Reeve. 



Species. 



8. bicornis, id. 



9. borealis, Linn. 



10. bullula, Reeve. 



11. cselata, id. 



12. calculus, id. 



13. Childreni, Gray. 



14. columbella, Lam. 



15. cornea, Reeve. 



16. dentifera, Jonas. 



17. digitalis, Lam. 



18. divaricata, Linn. 



19. eburnea, Reeve. 



20. edentula, C/temn. 



21. exasperata, Reeve. 



* The school of genus-makers represented formerly hy De Montford and Schumacher, then 

 hy Swainson, and now by Dr. Gray and the Messrs. Adams, is thus severely admonished by Messrs. 

 Forbes aud Hanley in their observations on the genus Lucina : — " Until our knowledge of the 

 tribe becomes much more minute and accurate than it now is, conchologists had better content 

 themselves with using a single generic term, than, through a false ambition of becoming the 

 parents of names, thrust worthless and embarrassing synonyms on a science already considerably 

 encumbered with rubbish." — Brit. Moll., vol. ii. p. 44. 



