30 BRITISH BELEMNITES. 



Hastati. Fusiform, with lateral grooves or canals. Lias and Oolite. 



A. Smooth. 



B. Unisulcate. 



C. With lateral canals. 



Each of the divisions thus indicated is subdivided into groups of allied species. 



M. Duval-Jouve proposed a classification limited to the Belemnites of the Neocomian 

 strata, which may be convenient for reference; though at the present time hardly a 

 single species of the groups he mentions and describes so carefully has been found in 

 England. 



1. Bipartiti. — The sides marked by a deep furrow, which divides them into two 



eqtlal parts ; place of the siphuncle unknown. JB. hipartitus of BlainviUe is an 

 example. 



2. Notosiphiti. — The siphuncle placed on the middle line of the dorsal asjied of the 



alveolus, opposite to the ventral canal of the guard ; always compressed ; the 

 opening of the cavity notched on the sides. 



3. Gastrosiphiti. — Siphuncle in the middle line of the ventral aspect ; always cylindric 



or depressed ; opening of the cavity terminating circularly or obliquely. 



Before proceeding further it is desirable to fix the meaning of a few terms of continual 

 use in describing the guard and phragmocone. In general figure a few Belemnites are 

 very nearly conical in the retral part of the guard, having there straight sides and a nearly 

 circular section ; more frequently the section is not circular, and the figure is better termed 

 conoidal. Again, in the middle of the guard, as usually found, some Belemnites are very 

 nearly cylindrical, with parallel sides and a circular section ; but as often other Belem- 

 nites have the section oval or in other ways deviating from a circle, and to such the term 

 cylindroidal will be applied. Looked at in a general sense, the whole form of the guard is 

 said to be Jiastate when between the apex of the phragmocone and the termination of the 

 guard the outline is swollen ; when this swelling is very slight the term subhastate may 

 be employed ; when, on the contrary, it is large and conspicuous the Belemnite is called 

 fusiform. Forms which are cylindrical or cylindroidal in the middle of the guard, and 

 conical or conoidal in the hinder part, are often conveniently called lanceolate. As 

 to the termination of the guard, it is in the Belemnitellae of the Chalk mucronate ; 

 in some Oolitic and Lias groups this form is nearly approached, and the term sub- 

 mucronate will be useful. In Belemnitella attenuata and some others the point is 

 produced ; and for the remaining forms acute and obtuse, with the help of the adverbs 

 very and sliyJdly, will probably suffice. For want of care in the use of two other terms 

 in respect of the guard, great confusion arises. Belemnites are compressed when the 



