LIMA. 37 



shallow groove mentioned in the description of L. elongata) there is another row of 

 similar, but slightly smaller spines. In the furrows between the main ribs there 

 are transverse ridges. 



On account of the close resemblance in the form and ribbing of L. echinata 

 to L. elongata, and also from the fact that in some specimens of the former the 

 ornamentation of the ribs is absent from a part of the shell and the ribs are then 

 indistinguishable from those of L. elongata, I am led to consider L. echinata as not 

 more than a variety of L. elongata. Further, in some specimens of L. elongata the 

 summits of the ribs are serrate. 



L. elongata var. echinata presents some resemblance toL. Schmeisseri, Wollemann, 1 

 from the Rhotomagensis-Plimer of Li'meburg. 



Types. In the Sedgwick Museum, from Burwell. 



Distribution. Totternhoe Stone (Holaster subglolosns zone) of Burwell and 

 Cherry Hinton. Also recorded in the ' Geological Survey Memoirs ' from the zone 

 of Schlwnlachia varians. 



LIMA (MANTELLUM) CANTABRIGIENSIS, nom. nov. Plate VI, figs. lOa, />, 11, 12. 



1881. LIMA ORNATA. R. Etheridge. In Penning and Juices-Browne, Geol. Cam- 

 bridge, p. 144, pi. iii, fig. 2 (non 

 ornata, d'Orbigny, 1847 ; lion 

 ornata, Buvignier, 1852). 



Description. Shell moderately convex, oval or rounded-oblong. Anterior 

 margin rounded. Umbones and ears not seen. 



Ornamentation consists of 16 or 17 main ribs with a few small ribs at the 

 posterior end. The anterior ribs are strong, roof -like, with ridged summits ; 

 posteriorly the ribs become less prominent and the interspaces less depressed. 

 Both ribs and grooves are ornamented with fine, well- developed ribs, which are 

 closer together on the ribs than in the grooves ; usually three or four occur on 

 each side of a main rib and three in each groove. Numerous concentric ridges 

 occur and give rise to spiny projections where they cross the fine radial ribs. 



Affinities. In form this appears to be similar to L. parallela (p. 28), but has 

 fewer ribs and is much more highly ornamented. The small rib at the bottom of 

 the groove is not distinguishable from the other ribs. 



It is more convex, has fewer ribs, and has the fine ornamentation better developed 

 than in L. intermedia. 



Remarks. This species is known by three specimens only. All are imperfect 

 near the umbo, but the fine ornamentation is well-preserved. 



' Abhaudl. d. k. preussisch. geol. Landesanst., 1ST. F.,' Heft 37 (1902), p. 55, pi. vii, fig. 9. 



