36 CRETACEOUS LAMELLIBRANCHIA. 



Affinities. — This species agrees in form with Lima gavltina (p. 31), but is 

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

 relatively broader and more distinctly limited, (3) by 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 Planer-kalk (Turonian) of Saxony figured as Lima 

 elongata by G-einitz seems to differ from this species in having fewer and more 

 rounded ribs, and in the ribs being more widely 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. elongata. 



Lima Astieriarm, d'Orbigny, is perhaps identical with L. elongata, but the summits 

 of the ribs appear to be somewhat more rounded. 



Lima Reussi, d'Orbigny (L. elongata of Reuss) seems to differ from L. elongata 

 in having a smaller apical angle. 



Remarks. — Under the name Plagiostoma elongata 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 been previously figured and described (but without 

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

 of Plagiostoma, elongata. 



Types. — 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 Holaster suh- 

 globosus. Chloritic Marl of Eastbourne and the Isle of Wight. Chalk Marl of 

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

 Zone of Holaster subglobosus of Blue Bell Hill (Burham), Stoke Ferry, and 

 Hunstanton. 



Lima (Mantbllum) elongata, var. echinata, Etherulge, 1881. Plate VI, figs. 8, 9 a — c. 



1881. Lima echinata, B. Etheridge. In Penning and Julces-Broivnc, G-eol. 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 L. 

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

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



