70 MOLLUSCA. 



rarely present. In the female Argonauta (fig. 543) there is a single- 

 chambered spiral shell with thin walls ; in Spirula (fig. 544) there is a 

 multilocular spiral shell, the chambers of which are traversed by a 

 siphon. 



Sub-order 1. Decapoda. In addition to the eight arms, there are 

 two long tentacles between the third and fourth pairs of arms 

 (ventral). The suckers are stalked and provided with a horny rim. 

 The eyes are without a sphincter-like lid. The mantle bears two 

 lateral fins, and at the mantle edge a well-developed 

 apparatus for closing the mantle opening. An internal 

 shell is present. 



Fam. Spirulidae. Spirula Pcronii Lam., Pacific Ocean. 



Fam. Belemnitidae. Selemnites digitalis Voltz, Upper Lias. 



Fam. Myopsidee. With closed cornea and covered lens. 

 Sepia qfficinalis Lam., Loligo vulgaris Lam., Mediterranean 

 (fig. 531). Sepiola vulgaris Grant., Mediterranean, Russia 

 macrosoma Fer. d'Orb., Mediterranean. 



Fam. Oigopsidae. Eyes with widely-opened cornea, so that 

 the crystalline lens is exposed and bathed by the sea-water. 

 Onychoteutliis Lichtenstcini Fer., OmmastrepTies todarus d'Orb. 



544 s i Sub-order 2. Octopoda. The two tentacles are not 

 Peronii present. The eight arms bear sessile suckers without 

 a horny ring, and are connected at their base by a 

 membrane. Eyes relatively small, with sphincter-like lid. The 

 short, rounded body is without the internal shell, and usually also 

 the fin-like appendages. Mantle without cartilaginous apparatus 

 for closing mantle opening, and attached to the head by a broad 

 cervical band. Funnel without valve ; oviduct paired. 



Fam. Octopodae (fig. 530). Octopus vulgaris Lam., O. macropus (fig. 535), 

 Eledone moschata Lam. 



Fam. Philonexidae. Philonexis Carence Ver., Tremoctopus violaceus Dell. 

 Ch., Argonauta argo L. The small male is without a shell (fig. 539). The 

 large female possesses fin-like expansions of the dorsal arms, and bears a boat- 

 shaped, delicate shell, round the sides of which the arm-fins are spread (fig. 543). 



