388 CEETACEOUS PELECYPODA 



This form is considered by its authors to be a sub-genus of Ambonichia, differ- 

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

 internal ribs have as yet been observed. 



4. Monopteria, Meek and Worth., 1866, (Palgeont. 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, Monopt. gibbosa, M. and 

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



This has been proposed as a sub-genus of Flerinea, 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 Monopteria to Hall's 

 AmpMccelia, which, they say, " was proposed as a sub-genus under Leptodomus^ 

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

 Fterinea^ though apparently generically distinct." 



5. Fteinnites, M^Coy, 1844, (Garb. Eoss. 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, 

 Ft, angustus, M^'Coy, from carboniferous beds. The shells referred to this genus 

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



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



a^ ^^4^ / 6. Bhynchopterus, M##k, 1864, (Pal. Calif, i, 31). Obliquely elongated, 



I tumid, anteriorly narrow, with a small acute ear, posterior side uniformly and slio'htlv 



j 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, diflPering from them by the absence of the posterior wins* 



The shell would also appear to have a close resemblance to Myalina, 



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

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

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

 surface concentrically sulcated, sometimes very finely radiately striated; type 

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

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

 cretaceous, or younger, deposits. 



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

 Obliquely broadly ovate, moderately compressed, equivalve or nearly so, hinge 

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

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



