Crick: A Rare Form of Actinocamax [A. Grossouvrei). 157 



The Yorkshire fossil is much depressed, especially its 

 posterior half, and is slightly curved towards the dorsal surface 

 (see fig". 2), just as is shown in the lateral aspect of M. Janet's 

 example {he. cit., PI. XIV., fig. ic). Its anterior end is imper- 

 fect, and shows no trace ot the alveolus. Its broad and not 

 very deep dorso-lateral grooves are well shown (see figs. 2 

 and 3), extending over fully three-fourths of its length. Its 

 surface, where not eroded, is quite smooth, and its ventral 

 portion exhibits the exfoliation of the superficial concentric 

 layers, as mentioned by M. Janet in his largest specimen. In 

 M. Janet's specimen, however, this exfoliation, doubtless result- 

 ing as that author points out from the imperfect calcification of 

 these layers, was most marked at the lower part of the ventral 

 surface, but in the present example it does not extend so far 

 back as the posterior extremity of the guard, and is due to the 

 imperfect calcification of almost the whole of the ventral portion 

 of the superficial layers. The calcified portions of these layers 

 cover, therefore, only the dorsal surface, the sides, and the 

 posterior part of the guard like successive sheaths, which are 

 open over the greater part of the ventral surface. (Two of these 

 sheaths are plainly visible in fig. i.) Possibly the present 

 specimen had not reached such an advanced stage of develop- 

 ment as M. Janet's largest example. 



The posterior part of M.Janet's examples was not sufficiently 

 well preserved to show if the guard possessed a mucronated 

 point, but though the point of the Yorkshire specimen is not 

 quite perfect, there is enough to show that the guard, as 

 Grossouvre* has already pointed out, was mucronated (see 

 specially fig. 3) as in Belemnitella nmcronata Schlotheim, 5/).,t 

 Actinocamax quadratus Blainville, sp.,\ and Actinoctunax siibven- 

 tricosiis Wahlenberg sp.% 



As M. Janet observes Actinocamax Grossoxivrei most 

 closely resembles Actinocamax subventricosus, Wahlenberg, sp. 



* Bull. Soc. geol. F"raiice, sen 3, vol. xxvii., No. 2, June, 1899, p. 129. 



t Taschenbuch fiir Mineralogie, torn, vii., 1813, p. iii. See also 

 C. Schliiter, Palaeontographica, Bd. xxiv., p. 80, pi. Iv., figs. 1-12. 



X M«^m. sur les Belemnites, 1827, p. 62, pi. i., fig. 8. See also C. 

 Schliiter, Palaeontographica, Bd. xxiv., p. 77, pi. liv., figs. 1-13 ; pi- liii-, 

 figs. 20-25. 



§ Petrificata Telluris Suecana (Nova Acta Reg. Soc. Scient. Upsal., 

 vol. viii., 1821), p. 80. See also C. Schluter^ Palaeontographica, Bd. xxiv., 

 p. 75, pi. liii., figs. i-g. 



1906 May I. 



