SUB-CLASS II DIBRANCHIATA 601 
with the ventral side concave, the coils not in contact, composed of nacreous substance ; 
septa concave; protoconch globular. Siphuncle ventral and marginal in position, 
completed by siphonal funnels extending between the septa. Prosiphon present. 
Recent ; inhabits tropical seas. [For description of the animal see “ Zoology,” Part 
LXXXIIL., of Challenger Reports, 1895.] 
Sub-Order B. SEPIOIDEA. Cuttle-fishes. 
Shell internal, without differentiated phragmocone and guard, but consisting essenti- 
ally of proostracum or “pen,” which is either oval, or narrow and elongated. Arms ten 
in number, provided with suckers or hooks. Ink-bag present. 
Family 1. Sepiophoridae. Fischer. 
Skeleton calewreous, elongated-oval, terminating posteriorly in a thickened mucro 
> ) 1 : 
which represents a rudimentary phragmocone and rostrum, and encloses a conical cavity. 
Siphuncle wanting. 
The thickened posterior mucro is a rudimentary structure probably corresponding 
to the guard of Belemnoids, and 
its conical cavity to the alveolus 
Belosepia retains a vestigial 
chambering but no siphuncele, 
and in Sepia a_ recognisable 
phragmocone is wholly wanting. 
Belosepia, Voltz (Fig. 1254). 
As a rule only the posterior 
portion of the proostracum is 
preserved. This ends in a bent 
spine, which is thickened an- 
teriorly, laterally expanded, and 
contains near the apex a conical 
alveolus. The latter shows on 
the dorsal side incomplete traces 
of septa, and a wide funnel-like 
depression occupies the place of a 
siphunele. Eocene; not uncom- 
mon in Paris Basin. 
Sepia, Lam. (Fig. 1255). 
Proostracum of equal length 
with the mantle, elongated-oval, 
rounded anteriorly, thickened 
posteriorly and terminating in a 
short mucro. The latter contains : ; aime Rd Pe 
a conical alveolus, External walls sgocone? “Auvers, near Paris, Ventral view of'shell. 4, Cal 
of proostracum consisting. of two 4; Foster, Sof eae a 
brittle calcareous laminae, the side (after Deshayes). mocone in front of mucro, 2/3. 
separated by a horny layer. In- 
ternally with a mass of extremely fine parallel calcareous lamellae, increasing in 
thickness anteriorly ; the lamellae separated from one another by minute vertical 
rods, thus producing a spongy texture. The familiar cuttle-bone of commerce or 
ossa Sepiae, is the pen of Sepia officinalis, Linn., and is found in great quantities 
along the coast of certain countries. Several Tertiary species known. 

Fia. 1254. Fic. 1255. 
