ACKPHALA TK8TACKA. 89 



which the hinge is not prolonged. We must be careful not to con- 

 found them with the Vulsellae *. 



VULSELLA, Lam. 



A little salient plate inside of the hinge of each side, from one of 

 which to the other extends the ligament, otherwise similar to that of 

 the Ostreae. By the side of this plate is a notch for the byssus, as in 

 the Mallei. The shell is elongated in a direction perpendicular to the 

 hinge. 



The most known species inhabit the Indian Ocean f. 



PERNA, Brug. 



Several parallel cavities across the hinge, opposed to each other in the 

 two valves, and lodging as many elastic ligaments; the irregular and 

 foliaceous shell marked on the anterior side and under the hinge by a 

 notch traversed by the byssus. The Pernae were also left by Linnaeus 

 among the Ostreae J. 



CRENATULA, Lam. 



The Crenatula?, lately separated from the Pernae, instead of having 

 transverse cavities on a broad hinge, are furnished with oval ones on 

 the very margin, where they occupy but little of its breadth. The 

 l>y-sus seems to be wanting, and they are frequently found among 

 sponges . 



It is thought that we may approximate to the Pernae, certain fossil 

 shells, in which the hinge is also furnished with cavities more or less 

 numerous, that correspond to each other, and thus appear to have fur- 

 ni>hed points of attachment to ligaments : thus those of the 



GERVILIA, Defr. 



Have a shell closely resembling that of the Volucellae, but with a 

 kind of double hinge, externally with opposed cavities, receiving as 

 many ligaments, and internally furnished with very oblique teeth in 

 r;u -h valve. Their impressions are found along with Ammonites in 

 compact limestone ||. The 



Ostrea tuhella, Chemn., VIII, Ixx, 657, of which the Ostrea anatina, Ib. 658, 

 659, is probably a mere accidental variety. 



f Mya tulsella, Chemn., VI, ii, To, 11 ; V. sponffiarum, Lam., Savig., Eg., Coq. 

 pi. xiv, f. 2 ; r. Mans, Lam., Sav., Ib., f. 3. 



J Ostrea tsoonomiim, Chemn., VII, lir, 584 ; O. pfrna, Ib., 580 ; O. Itgvmen, 

 Ib., 578; O. ephippium, Ib., Iviii, 576 ; O. mytiloidcs, Herm., Nat. fieri., Schr. 



II. ,v 



Ostrea picla, Gm., Chrmn.. \ II. Iviii, 575, or Crenatula phasionoptera, Lam., 

 ..-. Method., Test., pi. 216, f. 2 ; Crenatula acicularis, Lam., Ann. du Mus, III, 

 pl. ii, f. 3, 4 ; Cr. mytiloidts, Id., Ib. f. 1 and 2. See also the great work on Egypt, 

 Coq. pl. ii. 



|| Grrritta soleiwMes, Defr., Blainv., Malac., Ixi, 4 ; G. pernoldct, Dcslonchamp*, 

 S.H-. Lin. da Calvados, I, 1 16. G. siliqua, Id. Ib., &c. 



