LIMA. 21 



Brighton probably from Lewes. Mantell l regarded Plagiostoma Mantelli as a 

 synonym of his Plagiostoma Hoperi, and I think there can be no doubt as to the 

 correctness of that view. 



Geinitz (1872) considered Lima Hoperi of Sowerby to be distinct from L. Hoperi 

 of Mantell, thinking that the former (which he named L. Sowerbyi) was distinguished 

 by being almost smooth, whereas the latter is covered with radial grooves. The 

 smooth and the grooved forms agree exactly in shape, and between these extremes 

 in ornamentation every gradation may be seen. Moreover, although one of the 

 specimens figured by Mantell (fig. 3) is ornamented all over, the others (figs. 2, 15) 

 possess grooves on the sides only. I think, therefore, that there can be no doubt as 

 to the identity of L. Hoperi of Sowerby and L. Hoperi of Mantell. Further, it 

 should be noted that Sowerby's specimens were sent to him by Mantell as examples 

 of his L. Hoperi. 



The specimens figured by Geinitz (1872) as L. Hoperi (from the Planer-kalk of 

 Strehlen) are relatively higher (especially fig. 11) than Mantell's species, and are 

 probably examples of L. cretacea (see below). 



L. Hoperi of d'Orbigny 2 differs in having a smaller apical angle, in being 

 relatively higher, much compressed, and with the grooves more widely separated. 

 It may, however, be only a variety of L. Hoperi, Mantell. I have seen undoubted 

 examples of L. Hoperi, Mantell, from the Senonian of Marromme (near Rouen), 

 Lillebonne (Seine-Inferieure), and from other French localities. The form de- 

 scribed and figured by d'Orbigny as L. Mantelli is referred to below (p. 23). 



L. Lamberti of Peron, 3 from the zone of Micraster breviporus of Joigny, may be 

 only a variety of L. Hoperi. It is stated to differ chiefly in its greater length, but 

 in this respect it can, I think, be matched by some undoubted varieties of L. 

 Hoperi. 



For the relation of L. Hoperi to L. globosa see page 17, and to L. cretacea 

 see page 23. 



Remarks. This species varies considerably in the extent of the ornamentation. 

 Some examples are smooth, save for the pitted grooves near the umbo ; in many 

 cases the grooves are continued on to the sides of the shell ; less frequently they 

 extend to the middle of the valve, and may even reach the ventral margin. I 

 have not seen sufficient examples, of which the exact horizons are known, to enable 

 me to determine whether any of the varieties are characteristic of certain zones. 



Types. I have not seen the types. The specimens figured by Sowerby are in 

 the British Museum. The types, and also Sowerby's specimens, came from the 

 Upper Chalk (probably from the zone of Micraster cor-testudinarinm or the zone of 



*- 



1 'Trans. Geol. Soc.,' ser. 2, vol. iii (1835), p. 206. 



2 See Jukes-Browne, ' Quart. Journ. Geol. Soc.,' vol. Iii (1896), p. 152. 



3 ' Hist. Terr, de Craie' (1888), p. 151, pi. ii, fig. 1, 



