CRENATULA. 



Plate I. 



Genus CRENATULA, Lamarck. 

 Testa tenuis, subaquivahis, complanata, plerumque concm- 

 trke striata, Jibro-laminaris, obliqua. Cardo lateralis, 

 linearis, marginalis, crenulatm ; creiiis in seriem orcU- 

 natis, callosis, subexcavatis, ligamentum, excipieniihus. 

 Impressio miiscidaris oblmiga, indistincta. 

 Shell thin, nearly equivalve, smooth, mostly concentrically 

 striated, fibro-laminar, oblique. Hinge lateral, linear, 

 marginal, crenulated ; creuulcs set in a row, caDous, 

 rather hollow, receiving the ligament. Muscular im- 

 pression oblong-, indistinct. 

 This very characteristic genus was established about 

 half a century ago, by Lamarck, in the ' Annales du Mu- 

 seum' of Paris. It is a member of the family of Aviculacece, 

 and is distinguished by a narrow linear hinge, presenting 

 a row of hollow crenules or jutting cavities for the recep- 

 tion of the ligament. But concomitant with this are other 

 peculiarities of not inferior importance. The shells are all 

 of a delicate horny substance, and of a constant obliquely 

 quadrate or obliquely ovate growth; and it is their habit 

 to live imbedded in sponge. 



All the species ai-e from the Red Sea except a new one, 

 which 1 have the pleasure of introducing, of a very dis- 

 tinct typical form, from New Caledonia. 



Species 1. (Rg. 1 a and 1 b, Mus. Cuming.) 



Ceenatula nigeina. Oren. testa oblique ovatd, suhun- 

 dato-distortd, antice rotundatd, postice declivi-angu- 

 latd, nigrim, corned, concentrice interrupte plicaio- 

 striatd; radiis fuscescentibus distantibtcs undulatis sub- 

 ohscure pictd. 



The black Crenatula. Shell obliquely ovate, some- 

 what wave-distorted, anteriorly rounded, posteriorly 

 slopingly angled, black, horny, concentrically inter- 

 ruptedly plicately striated, rather obscurely painted 

 with waved, distant, brownish rays. 



Lamarck, Anim. sans vert. vol. vii. p. 72. 



Hub. Red Sea. 



Chiefly distinguished by its painting of distant faint 



brown rays upon a black horny ground. 



Species 2. (Mus. Cuming.) 

 Crenatula viridis. Oren. icstd transverse ovatd, sub- 

 obliqud, convexd, antice rotundatd, postice snbangulato- 



productd, teniii, concentrice striata; viridi, pallide 

 radiatd etfasciatd. 



The green Crenatula. Shell transversely ovate, rather 

 oblique, convex, anteriorly rounded, posteriorly an- 

 gularly produced, thin, concentrically striated ; green, 

 faintly rayed and banded. 



Lamarck, Anim. sans vert. vol. vii. p. 72. 



Hab. Red Sea. 



A species of delicate homy substance, easily recognized 



by its Anodon-\\k& form, and bright-green colour. 



Species 3. (Mus. Cuming.) 



Crenatula avicularis. Cren. testa trigono-flahellata, 

 declive utrinque angulari, versus umlones attenuatd, 

 dcpressd, concentrice interrupte pUcato-striatd ; ritfes- 

 cente-ttigrd, radiis linearibtts rufo-fnscis profuse pictd. 



The avicular Crenatula. Shell triangularly fan- 

 shaped, slopingly angular on each side, attenuated 

 towards the umboes, depressed, concentrically inter- 

 ruptedly plicately striated; reddish-black, profusely 

 painted with linear red-brown rays. 



Lamarck, Ann. du Mus. vol. iii. pi. 3. f. 1, 3. 



Hub. Red Sea. 



Distinguished by its sloping, angular form, and profuse 



brown-rayed painting. 



Species 4. (Mus. Cuming.) 



Crenatula bicostalis. Cren. testd subquadrato-ovatd, 

 antice convexd, rotundatd, postice concavd, abbreviato- 

 angtdatd, medio obscure radiatim bi-tricostafd, costit 

 subnodosis, concentrice striata ; nigra. 



The two-ribbed Crenatula. Shell somewhat squarely 

 ovate, anteriorly convex, rounded, posteriorly con- 

 cave, shortly angled, obscurely rayed in the middle 

 with two or three ribs, which are slightly noduled ; 

 black. 



Lamarck, Anim. sans vert. vol. vii. p. 72. 



Hab. Red Sea. 



In this spe(j)es there is a more characteristic difference 



between the convex anterior portion of the shell, and the 



concave posterior part, which describes a more contracted 



angle. About the middle, radiating from the umboes, 



there is a faint indication of noduled ribs. 



November, IS 



