77 



OX THE APERTURE OF A BACULITE FROM THE LOWER CHALK 

 OF CHARDSTOCK, SOMERSET. 



By G. C. Ceick, F.G.S., etc. 



Read Uth 3[arch, 1896. 



In 1876 Meek^ pointed out that tlie genus Baculites, as usually 

 understood, seemed to be divisible into at least two sections, according 

 to the nature of the aperture. In one division the aperture is 

 directed forwards, as in BacuUtcs vertehralis, Lara. ; in the other 

 it opens towards the antisiphonal side, as in BacuUtes haculoides 

 (Mantcll). 



Meek restricted the name BacuUtes to the former division, and 

 proposed for the latter section the name Cijrtochilas, observing that 

 " the direction of its aperture, and the curvature of the projection of 

 the siphonal margin of its lip, are such, that the head of the animal, 

 and other parts connected therewith, must have been protruded at 

 right angles to the longitudinal direction of the shell instead of on 

 a line with the same — a peculiarity that was probably accompanied 

 by important differences in the structure and habits of the animal." 

 Meek's views, however, with regard to the division of BacuUtes do 

 not seem to have met with general acceptance. 



As the type of his Cyrtochilus, Meek selected BacuUtes laculoides 

 (Mantell). The specimens hitherto figured showing this form of 

 aperture have usually been referred to Mantell' s species. In describing 

 this fossil in 1822 MantelP placed it in the genus Hamites. The two 

 specimens which he figured are now in the British Museum, but 

 neither of them show any trace of the aperture, although a con- 

 siderable portion of the body- chamber is preserved in each. 



Several authors have, however, since figured the aperture of speci- 

 mens which they have referred to Mantell's species; still, examples 

 showing the aperture are by no means common. 



The earliest figure appears to be that given by James de Carlo 

 Sowerby' in his "Mineral Conchology " in 1828. Under the name 

 BacuUtes ohUquatus, which he regarded as identical with Hamites 

 laculoides, Mantell, he figures and describes an example as "an 

 unique specimen, that shows the form of the aperture, which is 

 placed obliquely ; on each side is a large oval lobe, placed anteriorly 

 and bent backward." This specimen is now in the British Museum 

 Collection. It was without doubt this same specimen that Mantell 



' " United States GeoL Siirv. of the Territories," vol. ix, pp. 392-3. 



2 "Foss. S. Downs," 1822, p. 123, pi. xxiii, figs. 6 and 7 (B.M. Nos. 8,612 and 

 36,576 respectively). 



3 "Mineral Conchology," vol. vi, p. 186, pi. Dxcii, fig. 2 (B.M. No. 44,005). 



