406 CRETACEOUS LAMELLIBRANCHIA. 



Non 1842. Exogtra Boussinoaultii, ^. d'Orfcijrjii/. Voy. dans I'Amerique Mcrid., 



vol. iii, pt. 4, pi. xviii, fig. 20 ; 

 p , xxi, figs. 8, 9 ( = 0. Minos, 

 Coquaud). 



Description. — Left valve very convex, elongated between the ixrabo and the 

 postero-ventral extremity, more or less considerably arched, with a sharp carina 

 curving from the umbo to the extremity and becoming less prominent on the later 

 part of the valve. Behind the carina the valve is concave or flattened, in front of 

 it regularly convex. Umbo more or less considerably spiral. From the carina a 

 number of rounded radial ribs extend to the margin, but are indistinct or absent 

 on the posterior part of the valve ; these give a corrugated margin to the valve ; 

 the ribs are crossed by well-marked growth-ridges. Inside the valve, at a sliort 

 distance from the margin, is a band of transverse cremxlations. Adductor impression 

 large, oval, sulnnedian, or rather near the posterior margin. The attached surface 

 maybe small or large; when large, the marginal part (except the posterior) grows 

 vertically upwards from the support and bears ribs. Right valve nearly flat, with 

 growth-lines ; umbo small, spiral. 



AQinities. — This species is related to i?. if/wo.-*, Coquand,^ but in the latter 

 radial ribs occur on the right valve. It seems probable that E. tiihercuHfera has 

 been derived from a small form of E. sinuata. A small exam])le (Plate LXI, fig. 

 13) which agrees with the Isengata type of E. sinuata, except for the presence of 

 radial ribs, seems to connect that species with E. tuber culi/era.^ 



Types. — The type of Koch and Dunker is a right valve fi'om the Neocomian of 

 the EUigser Brink ; the surface of this specimen has a tuberculate appearance 

 because it is encrusted by another organism.^ Later authors have been able to 

 identify it with the forms named E. siihplicata, Romer, and E. BoussiiKjanlti, 

 d'Orbigny, of which good figures have been published. The specimens figured by 

 Forbes, which have a large surface of attachment, are from Atherfield, and are now 

 in the Museum of Practical Geology (No. 25984). 



Distribution. — Lower Greensand: — Perwa-bedof Atherfield, Redcliff (Sandown), 

 and East Shalford ; Crackers of Atherfield ; Ferruginous Sands of Shanklin ; 

 Hythe Beds of Lympne. 



1 D'Orbigny, ' Pal. Fran9. Terr. Crt-t.,' vol. iii (1847), pi. cccclxviii, figs. 1 — 3 ; Coquand, ' Mou. 

 Ostrea, Terr. Crt-t.' (1869), p. 183, pi. Ixiv, figs. 1—3, pi. Ixxiii, figs. 4^-8, pi. Ixxiv, figs. 14, 15 ; Pictet 

 and Campiche, ' Foss. Terr. Crt't. Ste. Croix' ('Mater. Pal. Suisse,' ser. 5, 1871), p. 278, pi. elxxxv ; 

 Wollemaun, ' Bivalv. u. Gastrop. deutsch. ii. holliind. Neocoms' (1900), p. 15; Miiller, ' Deutsch.- 

 Ost-Afrika,' vol. vii (1900), p. 548, pi. xxiii, fig. 1, text-figs. 46, 47. 

 - See also Leymerie (184'2), pi. xi, fig. 4. 

 3 The name tuberculi/era is consequently inappropriate, hut has [been retained by several authors. 



