688 



MOLLUSCA— CEPHALOPODA 



PHYLUM VI 



\>\ 



v(M-s, widest in front, rounded posteriorly, 



^niudinal line, and boimded on either side 



hyperbolic Striae. Ink-bag frequently preserved, 

 Contents transformed into a jet-like substance. 



Median area divided into 



by lateral areas with 



, the 



It is 



possible to dissolve the carbonaceous particles so as to 

 prepare a wash resembling India ink. Upper Lias of 

 Gennany, France and England. 



Beloteuthis Münst. (Fig. 1335). Proostracum very 

 tliin, elongated, feather - shaped, broadly rounded pos- 

 teriorly, pointed in front, traversed by" a median 

 longitudinal keel. Upper Lias of Würtemberg. 



Teuthopsis Desl. Lias. Kelaeno Münst. Upper 

 Jura. Phylloteuthis Meek and Hayden ; Äctinosepia 

 Wliiteaves, Cretaceous ; Cana,da. 



Plesioteuthis Wagner (Dorateuthis Crick) (Fig. 1336). 

 Proostracum very tliin, long, narrow, lanceolate, pointed 

 posteriorly, rounded in front, with a median longi- 

 tudinal keel and a raised line along each of the lateral 

 edges. Very abundant in the Lithographie Stone, and 

 impressions of the body and head not uncommon. Also 

 found in the Cretaceous of Maestricht and Syria. 



Order 3. OCTOPODA Leach. 



Body without internal shell, and only the female of 

 Argonauta secreting a single- Chamber ed external shell. 

 The two tentacles are not present, and the eight arms 

 bear sessile suckers without horny rims. Eye relatively 

 small, without sphincter-lihe lid. Body short and rounded^ 

 usually without fin-like appendages, 



The majority of genera belonging here are naked 

 and therefore without fossil representatives. The small 

 male of Argonauta Linn. is without a shell, but the 

 large female bears a delicate, boat- shaped, spiral shell 

 which is secreted partly by the mantle, and partly by 

 two fin-like ex^rnnsions of the dorsal arms. Outer surface 

 of Shell ornamented by folds and tubercles, and two 

 nodose ventral keels are present. Late Tertiary (Pied- 

 mont) and Recent. 



Galais J. de C. Sowb. Body short and round, 

 provided with triangulär lateral fins, not united behind. 

 I;ili\ely stout tentacular arms, these being of nearly uniform 

 length and .size, and each bearing a single row of suckers. This is the earliest known 

 üctopod genua Upper Cretaceous ; Mt. Lebanon, Syria 



Fig. 133(;. 



Plesioteuthis prism 

 Lithograpliic Stone ; 

 A, Impression of aini 

 arms and iiik-hjt.L;. /;, 



(liupi 



). 



list:MlL 

 liowin^- 



Head 



Sil 



\v\\ 



Vertical Range of the Dibranchiata. 



A. .•onipaml Mith Totraliranchiates, the Dibranchiata are of minor geological 

 '"•■'""•• ' l".ir ontuv Organisation renders them less well adapted for preserva- 



I 111 t 

 »ruAini 



lir n 



:.''■'. '^'."^ ■"■^■"nliiigly WC shall never be able to form even an 

 ,,„,,,,,„,,•. , f ;'"""■. ""l"^'tance m their contemporaneous faunae. The earliest 

 .op.cu.Ulu. of l>el..nn.o,dea appears in the Trias (Aulacoceras), ^nd the Sepioidea 



