388 CRETACEOUS PELECYPODA 



This form is considered by its autliors to be a sub-genus of Amhonichia, differ- 

 ino" from it by the very strong development of the posterior wing, on which no 

 internal ribs have as yet been observed. 



4. 3Io)ioi)teria, Meek and Worth., 1866, (Palseont. of Illinois, vol. ii, 339). 

 Obliquely sub-quadrate, sub-equivalve, moderately convex, with a large posterior 

 wing, being below the end generally insinuated, anterior wing obsolete or nearly 

 so, impressed below the beak, without a byssal emargination, but apparently 

 slightly gaping within the lunule ; muscular scars very faint ; hinge edentulous ; 

 ligamental area with a few longitudinal furrows; type, IfoiwpL gibbosa, M. and 

 W., supposed to be from carboniferous rocks of Illinois. 



This has been proposed as a sub-genus of Fterinea, but it appears to have 

 no internal hinge-ribs which characterize that genus. The authors speak of certain 

 ligamental furrows extending internally, but they are not shown in the figure of 

 the cast which in that part appears perfect. 



Meek and Worthen also refer to the relation of 3fono2)teria to Hall's 

 Amphicoelia, which, they say, " was proposed as a sub-genus under Leptodoimis, 

 to which it is not nearly allied. It evidently belongs to the Aviculibm, near 

 JPterinea, though apparently generically distinct." 



5. FteiHnites, M'^Coy, 1844, (Carb. Poss. of Ireland, p. 81). Sub-triangular, 

 anteriorly very narrow, becoming gradually wider posteriorly, equivalve, beaks 

 nearly anterior with a small gape below them, hinge line straight, as long as the 

 shell, edentulous, posterior end broadly truncate or very slightly sin uated; type, 

 Pt. angustus, M'^Coy, from carboniferous beds. The shells referred to this o-enus 

 are all of small size ; in general shape they strongly resemble Aviculojnnna, which 

 is, however, stated to be widely gaping posteriorly, like a Pinna. 



6. Rhynchopteriis, Meek, 1864, (Pal. Calif, i, 31). Obliquely elouo-ated 

 tumid, anteriorly narrow, with a small acute ear, posterior side uniformly and sliHitlv 

 curved, not distinctly winged ; hinge line straight, toothless, slightly thickened • 

 surface covered with concentric strise only; type, R. obesus. Meek, from triassic 

 rocks of California. This genus greatly resembles some of the mesozoic Aviculce 

 with smooth surface, differing from them by the absence of the posterior win"-. 

 The shell would also appear to have a close resemblance to Ilyalina. 



7. Fosklonomya, Bronn, 1837. Oblique, ovoid, or rounded, equivalve, very 

 much compressed, thin, hinge line straight, or nearly so, with sub-central slio-htly 

 prominent beaks, there being a short not emarginated wing on either side of them • 

 surface concentrically sulcated, sometimes very finely radiately striated ; type, 

 P. Bccheri, Bronn, from Devonian deposits. Species of this genus occur in 

 palaeozoic and lower and middle mesozoic rocks ; none are as yet known from 

 cretaceous, or younger, deposits. 



8. Moiiotis, Bronn, 1830, (Bronn's Jahrb. fiir Mineralogie, &c.. Sec, i, 284). 

 Obliquely broadly ovate, moderately compressed, equivalve or nearly so, hino'c 

 line straight, with the beaks sub-central and slightly projecting, anterior wino- 

 rounded in front, posterior oblique, truncate, or slightly insinuated ; surface radiately 



