PLEUROTOMARIA. 419 



riot the case with the fossils now under consideration. Yet for these d'Orbigny's 

 description and, to a certain extent, his figures answer exceedingly well. 



The following may be taken as representing the dimensions of British 

 specimens : 



Height . . . . .25 mm. 



Basal diameter . . . .30 mm. 



Spiral angle ..... 72°. 

 My specimens are somewhat smaller than the French ones, but the spiral 

 angle, shape, and ornamentation are almost identical. If there is any difference, 

 the whorls in d'Orbigny's figured specimen are rather more angular. 



The specimens which I refer to PI. amata occur principally at Louse Hill, in 

 the upper part of the Humphriesianus-zone. They evidently belong to the 

 Fasciatae, though restricted in size as compared with the bulk of that section. 



358. Pleueotomaria transilis, d'Orbigny, 185-1. Plate XXXVI, figs. 4, 4 a. 



1854. Pleurotomaeia transilis, d'Orbigny. Terr. Jur., vol. ii, p. 482, 



pi. ccelxxxvi. 

 Syn. — GTEOCTCLA, var. tbansilis, Deslongahamps. Vol. cit., 



p. 60, pi. vii, fig. 1. 



The specimen figured in the accompanying plate has a spiral angle of 58°, and 

 is without umbilicus. On the whole it tallies fairly well with the figures and 

 descriptions of the French authors, especially Deslongchamps, of this member of 

 the Gyroeyrfa- or FasciatM-groivp. There are two specimens in my collection from 

 the Parkinsoni-zone of Burton Bradstock. 



359. Pleurotomakia Alimena, d'Orbigny, 1850. Not figured. 



1850. Pleurotomaria Alimena, d'Orbigny. Prod., i, p. 208. 



1854. — — — Terr. Jur., vol. ii, p. 402, pis. 



ccclxxvii and ccclxxviii, fig. 1. 

 Syn. — gtroplata, var. jEQUISTRIATA, Deslongchamps. Vol. cit., 



p. 57, pi. vi, tig. 4. 



Since it is probable that the varieties sequistriata and inaequistriata merely 

 represent different stages or conditions of the same species, it might be permissible 

 to retain the specific name gyroplata. Provisionally, however, we may accept 

 d'Orbigny's name Alimena. 



