36 CRETACEOUS LAMELLIBRANCHIA. 



Affinities^. — This species agrees in form witli Lima gauUiva (p. 31), but is 

 distinguished (1) by the stronger ribs on tlic anterior area, (2) by the grooves being 

 relatively broader and more distinctly limited, (3) l)y the ribs being more elevated, 

 (4) by the fine radial ribs being usually indistinct except on the dorsal portions of 

 the shell. 



The form from the Pliiner-kalk (Turonian) of Saxonj' figured as JAma 

 elongata by Geinitz seems to differ from this species in having fewer and more 

 rounded ribs, and in the ribs being more Avidely separated on the posterior part of 

 the shell than elsewhere. Similar remarks apply to the specimen figured by 

 Fritsch. Without the opportunity of comparing specimens I am unable to give a 

 definite opinion as to the Turonian form being distinct from L. chmfintd. 



Lima AMerianii, d'Orbigny, is perhaps identical with Z. elongata, but the summits 

 of the ribs appear to be somewhat more rounded. 



Lima Beussi, d'Orbigny {L. ehngata of Reuss) seems to differ from Lj. elongata 

 in having a smaller apical angle. 



BemarJcs. — Under the name FJagiostoma ehngata Sowerby figured two species. 

 It seems advisable to retain the name elongata for the one shown in the lower of his 

 two figures, since that form had liecn previously figured and described (but without 

 a specific name) by Mantell, and Sowerby refers to Mantcll's figure as an example 

 of Plagiostoma elongata. 



T)jpe>i. — I have not seen the specimen figured by Mantell. Sowerby's type, 

 from the Chalk Marl of Hamsey, and also the specimen figured in Dixon's work are 

 in the British Museum. 



Distribution. — The range is from the Chloritic Marl to the zone of TTolaster snli- 

 glohof^ns. Chloritic IVIarl of Eastbourne and the Isle of Wight. Chalk Marl of 

 Ventnor, Folkestone, and Prince's Risborough. Totternhoe Stone of Arlesey. 

 Zone of IIola><t('r siihijliit)(i><n>< of l^luo Bell Hill (Bnrhani), Stoke Ferry, and 

 Hunstanton. 



Lima (Maxtelta-m) klonciata, var. echinata, Ethf ridge, 1881. Plate VI, figs. 8, 9 a — c. 



1881. Lima eohinata, R. Etheridgr. lu Penniiuj and Jukes-Browne, Geol. Cam- 

 bridge, p. 144, pi. ii, fig. 2. 



Remarks. — The examples described by Etheridge as Lima echinata agree 

 perfectly in form, in size, and in the number and character of the ribs with Tj. 

 elongata, but on the ridge at the summit of each rib there is a roAV of short spines 

 which are frequently rounded and stumpy, and on each side of the rib (outside the 



