30 CRETACEOUS LAMELTJBEANCHIA. 



more distinctly siiialk'r tluiii those on tlio anterior pnrt, nnd l)y tlie presence of 

 tlie small rib at the l)ottom of each groove. Sec also L. J'lii-i-iiiiiilniiri/sis (below). 



L. exjmnsa, Foi-bes,' fi-oni the ITythc Beds of Hythc, is known to me only from 

 the type specimen which is preserved in the Musenm of the Geological Society 

 (No. 2050). It is an internal cast in clay, somewhat crnshed, and shows the 

 ribbing only imperfectly. I think it is i)robal)ly an example of L. paralJcht, bnt 

 more specimens from the same horizon are needed Ijefore a confident opinion can 

 be given. Similar remarks apply to L. lingua, Forbes," which comes from the same 

 horizon and locality, and is likewise preserved in the Museum of the Greological 

 Society (No. 2058). 



This and the following eight species are provisionally referred to the sub-genus 

 Md 11 1 I'll urn, with which they agree in the form of the shell and, in many cases, in 

 the general character of the ornamentation. They differ, however, from the type 

 of Maidelliim in having the valves closed or almost closed, but there is, as Phillipi 

 has pointed out, every transition from the species in wliicli tlio \;ilves gape \vi<lcly 

 to others in which they are closed. 



I'riinirJrx. — This species shows a fair amount of variation in the ]iro]iortions of 

 length and height, and also in the obliquity of the shell. 



The type-specimen of L. 2^'i>'M''l'^ is an internal cast, and consequently all 

 writei's liave found it practically impossible to make out the charact(>i's of the 

 species from Sowerby's figure. A comparison of the type with better preserved 

 specimens leaves no doubt in my mind that Sowerl)y's species is really identical 

 with the form described by d'Orbigny as L. ('(itlnJiVuni. The latter author 

 I'cfei'red a species found in the Gault (/y. ijditHiiKi, p. ol) to L. pandlcla, Sowerby. 



'I'l/ji'-x. — The type is from the Ilythe Beds of Maidstone and is preserved in the 

 Hi'itish Museum (No. 4o,2i)2). The specimen from Upware figured as L. faniiiij- 

 (Idiit'iisis by Keeping is in the Sedgwick Museum, Cambridge. 



Dixfrihiitiou. — Prrna-hed and Atherfield Clay of Atherfield. Ferruginous Sands 

 of Shanklin. Hythc licds of Hythc, T.ympne, and Maidstone. Sandgate Beds of 

 Sevenoaks. Folkestone Beds of Folkestone, [jower Greensand of Faringdon and 

 Upware. Speeton Clay of Speeton. 



Lima (Mantktjjim) farringdonensis, Sharpr, 1853. 



1853. Lima farringdonensis, D. Sharpe. Quart. Jdiini. Gcol. Soc, vol. \, p. 198, 



pi. vi, fig. 2. 



Non 1883. — « — W. Keeping. Fuss., etc., Neoe. TJpware and ■Brick- 



hill, p. 112, pi. V, tig. 12. 



' 'Quart. JouiTi. Geol. Soe.,' vol. i (1845), p. 249, pi. iii, fig. 11. 

 - Ibi.L, p. 249, pi. iii, fig. 10. 



