6 CRETACEOUS LAMELLIBRANCHIA. 



nearly equal size, but sometimes (chiefly near the posterior border) with smaller 

 intercalated ribs. The ribs diverge slightly from a nearly median line, and bear 

 short spiny or scaly projections at regular intervals but not usually with a con- 

 centric arrangement. The spines are rather nearer the inner than the outer side 

 of each rib. The grooves are'narrow near the umbo but become broader in passing 

 ventrally, and at the ventral margin may exceed the ribs in breadth. The grooves 

 are rounded and (in some specimens) show transverse ridges. More or less distinct 

 growth-lines occur at intervals. 

 Measurements : 



(1) (2) (3) (4) (5) (6) 



Length . 25 . 21 . 20 . 17 . 16 . 14mm. 

 Height . 34 . 28 . 29 . 23 . 23 . 20 



(1, 3) Cambridge Greensand. 



(2) Base of Chalk Marl, Folkestone. 

 (4, 5) Upper Greensand, Warminster. 



(6) ,, Haldon. 



Affinities. This species belongs to the same group as the Senonian forms L. 

 Dunkeri, Hagenow, 1 and L. muricata, Goldfuss. 2 It is distinguished from the 

 former by its smaller apical angle and by the spines on the ribs being placed more 

 closely together. L. muricata differs from L. subovalis in having fewer ribs with 

 their ornamentation developed into long scale-like projections, and in having 

 oblique grooves in the interspaces. 



Remarks. A comparison of the type of Lima subovalis with examples of L. 

 ornata leaves no doubt as to their identity. The type-specimen of the former is 

 somewhat worn, but sufficiently w r ell-preserved for identification, and another 

 specimen on the same tablet shows the ornamentation quite clearly ; the shell is not 

 silicified, so that it was evidently not obtained from Blackdown the locality given 

 by Fitton but it has all the appearance of specimens found at Warminster. 



The examples from the Cambridge Greensand were referred to L. Rauliniana, 

 d'Orbigny, 3 by Mr. Jukes-Browne. The interior of these is filled with phosphate, 

 and the shell, although in some respects well-preserved, is rather abraded, so that 

 the remains of the spines usually appear as notches on the inner side (that facing 

 the median line) of each rib. The transverse ornamentation in the grooves is often 

 very distinct. Mr. Jukes-Browne has recently re-examined these specimens and 

 agrees with me in thinking that they cannot be separated from L. sulovalis. I 



1 ' Neues Jahrb. fur Min., etc.' (1842), p. 556 ; Vogel, 'Holland. Kreide ' (1895), p. 17, pi. i, fig. 9; 

 Eavn, 'Mollusk. Danmarks Kridtaflej.' (1902), p. 100, pi. ii, fig. 14. 



2 ' Petref. Germ.,' vol. ii (1836), p. 89, pi. ciii, fig. 4; Vogel, op. cit., p. 17, pi. i, figs. 10, 11. 



' Pal. Fran9. Terr. Cre't.,' vol. iii (1847), p. 542, pi. ccccxvii, figs. 58 ; ' Prodr. de Pal.' (1850), 

 vol. ii, p. 138 ; Pictet and Campiche, " Foss. Terr. Cret. Ste. Croix " (' Mater. Pal. Suisse,' ser. 5, 

 1869), p. 154, pi. clxvi, fig. 2. 



