282 -' Cehpalopoda in Tate and Blake’s 1 Yorkshire Lias.’ 
fragment. (See infra, p. 276). Indeed, fig. 5B does not represent the 
periphery of the specimen under consideration, for in this fossil the 
periphery is a little asymmetrical, and one side of the specimen is attached 
to matrix so that the exact width of the whorl cannot be seen. Another 
somewhat smaller example (about 60 mm. in diameter) in the same 
collection [B.M. No. C. 17898], and labelled in Blake's handwriting 
‘ Ammonites tardecrescens, base of MX. Robin H. Bay,’ has the periphery 
not only symmetrical but much better preserved. This, then, may have 
formed the basis of Blake’s figure 5B. 
Besides these examples there are other specimens in. the Blake col- 
lection. One [B.M. No. C. 19655], exposed on the surface of a split 
nodule and about 90 mm. in diameter, is labelled in Blake’s handwriting 
‘ A. tardecrescens, base of M.L. R. Hood’s B.,’ whilst a small specimen 
[B.M. No, C. 19656], 21 mm. in diameter, is labelled in the same 
handwriting : ‘ Armatus, R.H.B., Ammonites [tar] decrescens.’ An- 
other specimen, 17' 6 mm. in diameter [B.M. No. C. 19657] is unlabelled, 
but appears, judging from its lithological characters, to have come 
from the same horizon and locality. Further, a broken nodule, which, 
judging from the matrix, is apparently from the same horizon and locality 
as No. C. 19655, exhibits three specimens [B.M. Nos. C. 19658, C. 19659, 
C. 19660], the largest about 23 mm. in diameter. It was doubtless such 
forms as these which Blake had before him when he wrote : ‘ A small 
form is common in the same beds, which may be the young of this — it is 
the A. aureolus of Simpson.’ 
Arietites caprotinus d’Orbigny sp. (p. 286). 
Blake mentions one example from the ‘Zone of A. oxynotus, Peak,’ 
but there is now in the Blake collection no specimen either so labelled 
or comparable with D’Orbigny ’s figures (Pal. Franc. Terr. jur. I., PI. 
64, figs. 1, 2). 
Arietites sphioides d’Orbigny sp. (p. 286). 
In his remarks on this species Blake refers to five specimens from 
‘Probably zone of A. oxynotus, Robin Hood’s Bay,’ but the Blake 
collection does not contain a specimen either thus labelled, or that agrees 
with D’Orbigny’s figures (Pal. Franc., Terr, jur., I., PI. 64, figs. 3-5. 
Arietites spinaries Quenstedt sp. (p.,286). 
Of this species, Blake records ‘ fragments ; one good specimen in 
York Museum ’ from the ‘ Zone of A. Bucklandi, Robin Hood’s Bay,’ 
but the Blake collection now contains no example bearing this name. 
Arietites rotiformis J. de C. Sowerby sp. (p. 286). 
Blake states that ‘ A fine specimen of this species, which differs 
from A. bisulcatus in haying narrower whorls, and from A. multicostatus 
in having tubercles on the outer side, in the Leckenby Collection is the 
authority for inserting' it in the list,’ giving for the ‘ Geological position ’ 
of the species : ‘ Probably zone of A. Bucklandi (1 ex.).’ There is 
now in the Blake collection no example marked as referable to this, 
species. 
Arietites turneri J. de C. Sowerby sp. (p.,286). 
Blake states that ‘ With this species are identified some of the very 
large Ammonites found on the lowest scars at Robin Hood’s Bay. In 
extreme age they are not easily distinguished from A. stellaris ; in the 
latter the whorls grow narrower, in this broader.’ The Blake collection 
now contains no specimen which has-been identified with this species, 
the ‘ Geological position ’ of which Blake gives as : ‘ Zone of A. Buck- 
landi (upper part). Redcar, Robin Hood’s Bay.’ 
Arietites sinemuriensis d’Orbigny sp. (p. 287). 
Respecting this species Blake merely states : ‘ Similar to A . bisulcatus 
Naturalist 
