BIVALVIA. 163 



1. Crassatella Bartonensis, Edwards MS. PI. XXIV, fig. 7 a, h. 



Spec. Char. Or. Testa orhiculato-trigonuld, crassiusculd, subaquilaferali, compressd ; 

 regulariter sulcata vel lamellatd ; lamellis distantihiis, siniplicibus ; umbonibus acutis 

 elevatis ; pedi-regione vix minore ; ani regione superne declivi ; lunula minima, depressd, 

 lavigatd ; cardine brevi ; in valvd dextrd unidentato, valvd sinistra bidentato ; dentihus 

 lateralibiis elongatis ; marginibus integris. 



Shell roundedly trigonular, not very thick, nearly equilateral, compressed, externally 

 sulcated or laminated ; ridges distant, rounded and depressed ; beaks sharp and prominent ; 

 pedal region a trifle the smaller of the two; dorsal margin sloping; lunule small, 

 depressed, elongated ; hinge short, denticles sharp ; lateral teeth narrow, elongated ; 

 margin smooth. 



Diameter, fths of an inch. 



Locality. Barton [Edwards). 



Two specimens of this species are all that I have seen, and they are both from the 

 same locality. The principal distinction is the exterior ornament, the ridges or lamellae 

 being more distant than on any other of the suborbicular species of this genus. These 

 ridges are very regular and cover the entire surface. The diagonal ridge on the siphonal 

 or anal side, so conspicuous on the transverse species, is scarcely perceptible. 



2. Crassatella Bronnii (?), Merian. PI. XXIV, fig. 2 a — c. 



Crassatella Bronnii, Merian. In Litteris Sandb., 1853, sec. Deshayes. 



— — Desk. An. sans Vert, du Bass, de Par., vol. i, pi. xix, figs. 12 — 14, 



and pi. XX, figs. 22—24, 1860. 



Spec. Char. Cr. Testa minima, ovato-trigond, incequilaterali, transversim sulcata; 

 umbonibus minimis, acutis, proeminentibus ; latere antico breviore ; postico subtruncato , 

 lunula minima, depressd, lavigatd, ovato-lanceolatd ; cardine brevi, bidentato, altera uniden- 

 tato, dentihus angustis, elongatis ; marginibus integris. 



Shell small, roundedly trigonal, slightly inequilateral, covered with regular and rather 

 close-set concentric ridges ; beaks small and somewhat prominent, sides unequally 

 rounded ; lunule small, smooth and ovately elongate ; hinge narrow, one tooth in the 

 right valve and two in the other ; margins smooth. 



Diameter, ^ an inch. 



localities. Highclifl', Barton, Stubbington (Edwards). 

 France: Jeures, Etrechy [Deshayes). 



