ACEPHALA TESTACEA. 397 



Plagiostoma, Sowerb. 



The oblique shell of a Lima, flattened on one side; very small ears; 

 the valves more convex, striated, without scales, the opening for the 

 byssus smaller(l). Found in formations anterior to chalk. 



Pachytes, Defr. 



Nearly the same form as that of the Pectines; shell regular, with 

 small ears; a flattened transverse space between their summits, 

 which in one of the valves is marked by a deep triangular notch, in 

 which passed the ligament. Found in chalk(2). In the 



DiAxcHORA, Sowerb., 



The values are oblique and irregular, one of them adherent and with 

 a perforated summit, the other free and with ears(3). 



PoDOPSis, Lam. 



Regular striated valves without opercula; the summit of one of them 

 more salient, truncated and adherent, frequently very thick, and 

 forming a sort of pedestal to the shell(4). 



Although raultivalvej we should approximate the 



Anomia, Brug. 



To the Ostrese. The Anomise have two thin, unequal, irregular 

 valves, the flattest of which is deeply notched on the side of the 

 ligament, which is similar to that of the Ostrese. The greater part 

 of the central muscle traverses this opening to be inserted into a 



scribes a fourth living species under the name of Hinnita Defrancii; M. Defrance 

 also admits two fossil species, the H- Cortesii, Blainv., Malac, pi. lxi,f. 1, and the 

 H, Dubmssonii. 



(1) Plagiostoma gigas, Sowerb., Encyc. Method., Test., pi. 238, f. 3; — PI. Ise- 

 vigatum. Parkins., Org. Rem., Ill, pi. xiii, f. 6; and the other species given by 

 Sowerby, Min. Conch., pi. 113, 114, and3S2. 



(2) Pachytos sj)i7iosus, Fr. Sowerb., Cuv., Oss. Foss., II, Env. de Paris, pi. iv, 

 2, A, B, C, and Ulainv., Malac, pi. Iv, f. 2: — Pack, hoperi, Sowerb., 380. 



(3) Blanch, striata,- — D. lata, Sowerb., Min. Conch., pi. 80. 



(4) Podops. truncata, Encyc. pi. 188, f. 2, 6, 7; Cuv., Oss. Foss.; Env.de 

 Paris, pi. V, f. 2. 



N.B. M. de Blainville considers these four last genera as more nearly related to 

 the Terebrutulac. M. Deshayes, on the contrary, Ann. des Sc. Nat. Dec. 1828, ap- 

 proximates them to the Spondyli. 



