OF SOUTHEEN INDIA. 475 



whether all the Jurassic species referred to Flacunopsis agree with the character- 

 istics above noticed ; many of them appear to belong to Anomia, and doubts are 

 expressed on this point even regarding the type species, P. Jurensis. 



2. Cydostreon, Eichw., 1867, (Leth. ross., xme livr., p. 406). Shell obliquely 

 ovate with attenuated obtuse beaks, inequivalve ; one (right ?) valve convex ; the 

 other (left ?) smaller, flat or concave, with a small transverse ligamental groove 

 at the apex ; in the convex valve there is only a small lateral groove below the 

 beak, placed somewhat anteriorly ; both beaks are truncate and appear to indicate 

 an attachment to foreign bodies ; muscular impression indistinct, represented by a 

 marginal zone which surrounds the cavity of the convex valve. In the figure given 

 by Coquand (Monog. Ostrea, pi. xiv, figs. 10-14), the whole of the internal part 

 of the valves seems to be occupied by one large impression. Type, Ostrea Mlssoni, 

 Hag., C= Ostrea pUcatuloides, Leymerie). This shell greatly resembles Hemi- 

 plicatula, but is stated to have no such hinge or cartilage ribs as are characteristic 

 of that genus. 



3. Faranomia, Conrad, 1860, (Journ. Acad. Nat. Soc, Phil., iv, p. 290, and 

 Am. Journ. Conch., iii, p. 8). Irregular, inequivalve ; one valve flattened or 

 slightly concave, hinge of lower valve with a broad, irregular, triangular tooth or 

 plate, flattened or slightly convex, with sharp margins and an anterior, compressed, 

 small, but prominent tooth; muscular impression situated towards the ventral 

 margin in a line with the apex, or nearly equidistant from the anterior and posterior 

 ends. Type, Flacunanomia Saffordi, Con., from cretaceous rocks of Tennesee. 

 There are only two other cretaceous species which Conrad refers to the same genus ; 

 it seems to be closely allied to Philip pi's Fododesmus, The convex valve has no 

 teeth or appendage and is generally radiately ribbed ; the flatter valve is often 

 attached near the umbo to other objects and very thin, but not perforated. 



4. Carolia, Cantr., 1838,* (Bull. Acad. Bruxelles, v, p. Ill, Hemiplacuna, 

 Sow., 1849, teste Gray). Shell sub-orbicular, sub-equivalve, compressed, in 

 general structure, and in the fine radiating ornamentation, resembling Flacuna; 

 one valve flattened, the other slightly convex, with a distinct sub-marginal umbo ; 

 hinge in the flatter valve consisting of a strong sub-triangular tooth, somewhat 

 irregularly plicated at the base, above raised, and on either side with a sloping 

 elongated surface to which the ligament attaches itself, corresponding in the 

 other valve to two diverging flat ridges joined below the umbo; the whole of 

 the upper hinge margin is flattened and concentrically rugosely striated. A short 

 groove runs from the umbo to the margin (similar to that of Enigma) ^ and at 

 certain stages of age there appears to be a temporary short vertical slit below 

 the tooth of the flatter valve ; muscular scar round, sub-central. Type, C, pla- 

 cunoides, Cantr., (supposed to be) from tertiary beds of Egypt. Woodward 

 (Man., p. 410,) states that there is in the young shell of this type species a narrow 

 vertical byssal foramen below the hinge-tooth of the flatter valve, but that it 



* Non Carollia, Gray, 1838. 



