66 



mentary pit, and the utmost inclination that any species has to be- 

 come lobed, excepting the two well-known cross-lobed species known 

 as the Hammer Oysters. 



Genus 4. PERNA, Lamarck. 



Animal; mantle prolonged behind, with the lobes free throughout ; 



foot conical, carrying at its base a rough large byssus. fDes- 



hayes.J 

 Shell ; fat, nearly eauivalve ; umboes small, often terminal and 



hooked ; hinge broad, marginal, deeply cut with parallel grooves 



contai7iing the ligament ; posterior opening for the passage 



of the byssus conspicuous. 



The Perna are variously shaped, round, pectinate, or winged, but the 

 genus may be at once recognized by the peculiarities of the hinge. It 

 takes the form of a broad marginal plate cut across with great regularity 

 by parallel grooves, and the intermediate ridges of the valves do not inter- 

 lock with each other, like teeth, but press in contact, leaving the cavities 

 between them for the reception of the ligament. 



The shells of Perna have a strong affinity with those of Malleus in re- 

 spect of growth, but the hinge is of quite a different structure. They are 

 chiefly from the Eastern Seas. A few are from the West Indies and from 

 the Islands of the Pacific. 



1. Anomioides, Reeve. 



2. attenuata, id. 



3. Australica, id. 



4. Californica, Conrad. 



5. caudata, Reeve. 



6. costellata, Conrad. 



7. Curningii, Reeve. 



8. eplrippium, Linn. 



9. fiinbriata, Reeve. 

 10. imbricata, id. 



Species. 



11. isognomum, Linn. 



12. laticostata, Reeve. 



13. legumen, Gmel. 



14. lentiginosa, Reeve. 



15. Limoides, id. 



16. lingiiiformis, id. 



17. lobata, id. 



18. marsupium, Lam. 



19. nucleus. Lam. 



20. patibulum, Reeve. 



21. pectinata, Reeve. 



22. quadrangularis, id. 



23. rudis, id. 



24. semiuuda, Lam. 



25. serratula, Reeve. 



26. spatliulata, id. 



27. vespertilio, id. 



28. vitrea, id. 



29. Vulsella, Lam. 



Figure. 

 Perna Australica. PI. 29. Pig. 168. Shell, with the upper valve 



