ACKl'HALA TKbTACKA. 87 



PLAGIOSTOMA, Sowerb., 



The obli.jue shell of a Lima, flattened on one side; very small ears ; 

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

 smaller *. Found in formations anterior to chalk. 



PACHYTKS, Defr. 



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

 smill ears; a flattened transverse space between their summits, 

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

 which paed tin- ligament. Found in chalk f. In the 



DIANCHORA, Sowerb., 



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

 a perforated summit, the other free and with earsj. 



PODOPSIS, Lam. 



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

 inure salient, truncated and adherent, frequently very thick, and form- 

 ing a sort of pedestal to the shell . 



Although multivalve, we should approximate the 

 ANOMIA, Brug. 



To the Ostreae. The Anomiae 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 Ostreae. The greater part 

 >1 the central muscle traverses this opening to be inserted into a 

 third plate that is sometimes stony and sometimes horny, by which 

 the animal adheres to foreign bodies, and the remainder of it (the 

 muscle) serves to join one valve to the other. The animal, ECJHION, 

 Poli, has a small vestige of a foot, similar to that of a Pecteri, which 

 slips between the emargination and the plate that closes it, and per- 

 haps serves to direct water to the mouth which is close to it ||. 



These shells are found attached to various bodies like the Ostreae. 

 They are found in every sea ^f. 



* I'Utyioitoma giyas, Sowerb., Encyc. Method., Test., pi. 238, f. 3 ; PI. Ue- 

 rii/nhnn, Parkins., Org. Rein.. Ill, pi. xiii, f. 6 ; and the other species given by 

 Sowerby, Min. Conch., pi. 1 13, 114, and 382. 



f Pachiifia sinnnsus, Fr. Sowerb., Cuv., Oss. Foss., II, Env. de Paris, pi. iv, 2, 

 A, B, C, and Hlainv., Malar., pi. Iv, f. 2: Path, hoperi, Sowerb., 380. 



J Dianch, striata ; D. lata, Sowerb., Min. Conch., pi. 80. 



Pwiopt. tntncata, Encyc. pi. 188, f. 2, 6, 7 ; Cuv., Oss. Foss. ; Env. de Paris, 



pl. V. f. I, 



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

 the Terebratulte. M. Deshayes, on the contrary, Ann. des So. Nat. Dec. 1834, it 

 proximate thorn to the Spondyli. 



|| This foot escaped the notice of M. Poli. 



HUM ephippium, Gin.. .!. ctjm ; A. elcctrica ; A. squamula; .1. acu- 

 l,-tilit .- .1. siitninnt . .1. / t'nctata ; A. umlulata, und the species added by Ilru- 



.-. Mr'!-... I.. \ M~.. ! TO, , t ieq, . ai (1 |il. I/O, 71. 

 The other Anomi* of Gmelin arc Placun<r, TtrcbraitUr, and Hyaler. 



