53 



several are truncated, terminated by a smooth convex surface ; 

 mouth oval, furnished ivith large divided lips, having on each 

 side a pair of oblong-pointed labial palps ; branchite doubled 

 over, formed of detached f laments ; foot rudimentary, with a 

 club-like pedicle at its disc. (Deshayes.) 

 Shell ; affixed, inequivalve, irregular, more or less auriculated, 

 radiately striated and ridged, rarely ribbed, variously prickled 

 and spined ; umboes equal, separated by a very large flat area, 

 more and more produced with age ; hinge, with two solid re- 

 curved teeth in each valve, strongly interlocking and receiving 

 the ligament between them. 



One of the first shells that attracted the attention of the Father of Na- 

 tural History on the shores of the Mediterranean was the beautifully spined 

 Thorny Oyster, Spondylus gadaropus. There it still lives in all its royal 

 panoply of purple and white ; and the name which Aristotle gave to it 

 more than two thousand years ago remains to this day. Nearly seventy 

 species from different parts of the globe are now associated with it in the 

 genus, and all have their peculiar type of form and sculpture. The growth 

 of the Spondyli varies, like that of the Ostrea, according to the irregu- 

 larities of their place of attachment, but the shell is of firmer substance, 

 and the larger concave valve being the lower, the upper valve is left free 

 for the development of the variously ramified fronds, spines, and prickly 

 scales by which the species are so profusely ornamented. 



It is curious to observe how in many Spondyli the upper valve advances 

 with the animal in its progress of growth without change, while the lower 

 valve, being affixed, is added to by successive layers upon layers. An um- 

 bonal area is often thus formed of very considerable extent, the hinge and 

 ligamentary pit being pushed forward with the advancing growth ; and 

 water sometimes becomes hermetically sealed between the layers, moving as 

 freely between them as in a spirit-level. The following is a list of the 

 Spondyli described and figured in the ' Conchologia/ 



1. aculeatus, Chemn. 



2. affinis, Reeve. 



3. albibarbatus, id. 



4. Americanus, Lam. 



5. asperriruus, Soto. 



6. aurantius, Lam. 



Species. 



7. barbatus, Reeve. 



8. basilicus, id. 



9. Butleri, id. 



10. camurus, id. 



11. candidus, Lam. 



12. castus, Reeve. 



13. ciliatus, Brod. 



14. coccineus, Lam. 



15. croceus, Chemn. 



16. Cumingii, Sow. 



17. cuneus, Reeve. 



18. digitatus, Sow. 



