270 CRETACEOUS PELECYPODA 



close together, sub-anterior ; anterior muscular impression oval, distinct, with 

 a small groove above it, and both posteriorly bounded by a prominent ridge, 

 posterior muscular scar faint ; cardinal margin internally thiclvcned the whole 

 length, probably for the support of a ligament ; surface concentrically (or radiately ? 

 sometimes partially) striated or sulcated; type, S. discors, M'Coy. Only palaeozoic 

 species are referred to the genus; some of them are in external form almost 

 identical with Fharella, and it as yet remains to be shown whether there are in 

 Sanr/uinoUies any hinge-teeth present or not. In the Brit. Pal. foss., (p. 276), 

 M'^Coy considers this genus apparently identical with King's Allorisma, stating 

 that King " supposed them to be sinupallial, which certainly is not the case in the 

 palaeozoic shells," &c. We can only say again that unless King's statement 

 and apparently correctly executed figures are disproved, the identification of the 

 two genera must be set aside as inadmissible. 



4. Leptodomus, M'Coy, 1844, (Carb. foss., Ireland, p. 66, and Brit. Palseoz. 

 foss., p. 277). Shell oblong, somewhat trapezoid, tumid, very thin, anteriorly 

 rounded, beaks sub-anterior, posteriorly sub-truncate and gaping, concentrically 

 sulcated ; beaks incurved witli a somewhat excavated lunule below ; hinge without 

 teeth, the posterior hinge-line more or less straight, muscular and pallial impres- 

 sions faint; type, L. fra(jilis, M'^Coy. The species are all palaeozoic ; those with a 

 median sulcus extending from the beaks to the ventral edge seem to be more correctly 

 referable to Grammysia ; the typical forms greatly resemble some Tnqjezla 

 (== CypricardiaJ, but are readily distinguished from them by their thin shells. 



5. Orthonota, Conrad, 1841, (1827 ?). Shell narrow, like a Fharella, with 

 sub-parallel upper and lower margins, very inequilateral, the beaks being sub- 

 anterior and tumescent, lunula in front (?) of the beaks somewhat excavated, 

 very thin, surface posteriorly generally undulatcly striated, hinge aj)parently 

 without teeth. Conrad (Am. Journ. Conch., 1866, ii, p. 103,) says that the type 

 of this genus is O. tmdiilata, Con., and quotes Scmgidnolltes anyuUferus and 

 iridinokles of M^Coy among the European representants of the genus. Since 

 the name was introduced, there appear to have been several other species referred 

 to it with a crenulated or toothed hinge-line, and wliich seem to lie identical with 

 the shells called by King Bakevellia. 



6. Anodonto2:)sls, M^Coy, 1851, (Ann. Mag. Nat. Hist., vii, p. 53, and Brit. 

 Palseoz. rocks and foss., p. 270). Shell rather compressed, sul)-trigonal or trapezoid, 

 anteriorly generally somewhat narrowly rounded, posteriorly obliquely truncate, 

 hinge rectilinear, shorter than the length of the shell, with an internal posterior 

 marginal rib, double in the right valve, and a second shorter rib in front of the 

 beaks ; a small cardinal tooth is said to be occasionally present below the beaks ; 

 muscular scars ovate, the posterior larger and stronger than the anterior ; jmllial 

 line entire; type, A. anff uslif rons, M.'Coj. Salter suggested for ^, secM/'Z/b;'//**'*, 

 M'Coy, and allied forms, the name Fseudaxinus. 



7. Sedgwickia, M'Coy, 1844, (Carb. foss. of Ireland, p. 61). Elongated, 

 inequilateral, anteriorly rounded and shorter, posteriorly sub-truncated, moderatelj'- 

 tumid, with incurved beaks, anterior half of the surface ornamented with con- 



