DECAPODA 



387 



apical line, which extends from the extremity of the pliragmoconc 

 to that of the rostrum. DistribuHon, see p. 380. 



Fam. 1. Spirulidae. — Arms with acetabula, shell a loose 

 spiral, without rostrum or pro-ostracum, partially external, 

 enclosed in two lobes of the mantle (Figs. 247 and 248). 



Tlie single species of the single genus (*S'. Peronii Lam. = laevis 

 Gray) has not yet been thoroughly investigated, although the 

 shell occurs in thousands on many tropical beaches, and is some- 

 times drifted on our own shores. The animal appears to ]ia\e 

 the power of adhesion to the rocks by means of a terniinal sucker 

 or pore. The protoconch is present, 

 and contains a prosiphou, which does 

 not connect with tlie sipli uncle. The 

 septal necks are continuous, not broken 

 as in Nautilus. The siphuncle is on 

 the ventral margin of the shell, the 

 last whorl of which projects slightly on 

 the dorsal and ventral sides, but is 

 even there covered by a thin fold of 

 the mantle. The retractor muscles of 

 tlie funnel and of th(! head find their 

 puiid iVappid on the shell, the last 

 chamber of whicli contains the pos- 

 terior part of the liver, with whicli the 

 mendjranous si])lnuicle is connected. 



Fam. 2. Bch'innitidae. — Arms hooked 

 as in Onyclioteuthis, fins large ; phrag- 

 mocone straight, initial chamber globu- 

 lar, larger than the second, rostrum 

 often very long, investing the plirag- 

 mocone, pro-ostracum sword- or leaf- Fig. 2iQ.— Sepia officinalis L., 



, , ^ ^ • i> L 11 with mantle cut away to 



shaped, rounded m front, seldom pre- ^^^^^ position of internal 

 served, hdv-sac ])resent. — Lower Lias «i'eil- x^- (The ends of the 



tentacular arms are cut off.) 



to ( retaceous. 



The Lelemnitidac are l)elieved to have been gregarious, and to 

 have lived in shallow water on a muddy bottom. Specimens are 

 sometimes found in which even the ink-sac can be recognised in 

 situ. The relative ])ropoi'tions of rostrum and phragmocone vary 

 greatly in different groups, the rostrum Iteing in some cases 

 two feet long, in others only just enclosing the ]>hi'agmoconc. 



