above the phragmocone. 
596 MOLLUSCA SUB-KINGDOM VI 
phragmocones almost always occur detached. The former originally mistaken for 
Orthoceratites, but are distinguished by their marginal siphuncle and characteristic 
conothecal striae. [Hyatt regards both Auwlacoceras and Atractites as descended from 
Orthoceratites.] Upper Trias and Lias of the Alps. 
Xiphoteuthis, Huxley. Lower Lias; England. 
Belemnites, Lister (Figs. 1237-1242). 
Name first applied by Agricola in 1546. 
Guard dactyliform, subcylindrical, or 
conoidal, sometimes short and thick, sometimes 



Ph 
as 
aS. 

tt 
\ 




Th 
T ! 
eT 
i 

| 
ene 
\y) 

Fia. 1237. 
A, Vertical section of a Belemnite, the proostracwn broken away 
Fie. 1238. 
B, Belemnites Brugierianus, Miller. Lower Aulacoceras reticulatum, Hauer. 
Lias; Charmouth, England. Cast of complete individual. 1/; (after Upper Trias; Réthelstein, near 
Huxley). C, Restoration of a Belemnite shell. Aussee, Austria. A, Guard and 
Abbreviations: R, Rostrum or ‘guard’; Ph, Phragmocone; Po, phragmocone, 2/3. B, Guard, 1/;. 
Proostracum ; a, Apical line reaching from apex of guard to bottom of C, Portion of phragmocone sliced 
alveolus (0); 6, Impression of arms ; c, Camerae of phragmocone ; 7, An- 
; to show siphuncle and siphonal 
terior end of proostracum ; 0, Protoconeh ; si, Siphuncle; a, Ink-bag. 
funnels. 
slender and much elongated; retral portion tapering, submucronate, or obtusely 
rounded. Owing to irregularity in secretion of calcite layers on the periphery of the 
guard during growth, individuals belonging to the same species but of different ages 
are apt to vary considerably in form. Such differences are well illustrated in B. 
acuarius, Schloth. The young are sometimes fusiform, but grow cylindrical or 
conical with age. About 350 species are known, ranging from the Lower Lias to 
summit of the Cretaceous; maximum from Middle Lias to Lower Cretaceous. 
