390 



DECAPODA 



CHAP. 



tentacular arms with four ; fourth left arm hectocotylised at the 

 tip ; funnel attached to the head. Other genera are LoUguncula, 

 Sepioteuthis^ and Loliolus. Belemnosepia^ Beloteuthis^ Leptotew- 

 tliis^ and Phylloteuthis are fossil genera only, differing in the 

 shape of the gladius. 



(5) Oigopsidae : cornea more or less open ; species pelagic, 

 Fam. 5. Ommastrephidae. — Body cylindrical, fins generally 

 terminal, united together, regularly rhomboidal, sessile arms 

 with varying number of rows of acetabula, mantle connexions 

 elaborate; gladius horny, narrow lanceolate, with a hollow 

 cone at the posterior end. — World-wide. 



Ommastrephes proper has a natatory web on the sessile arms ; 

 the wrist of each club has a series of acetabula with correspond- 

 ing cushions on the other wrist. In Thysanoteuthis (often made 

 a separate family) the sessile arms have two rows of cirrhi, with 

 lateral expansions of the skin ; fins as long as the body. In 



Fig. 250. — Architeuthis princeps, Verr., E. America: /, Right fin; fu, funnel; f.c, 

 fixing cushions and acetabula on the tentacular arms (t, t). (After Verrill, x 5^5.) 



Architeuthis, to which belong the largest Cephalopoda known, 

 the fins together are shaped like a broad arrow-head ; acetabula 

 of sessile arms strongly denticulate ; tentacular arms very long, 

 with equidistant pairs of acetabula and fixing cushions through- 

 out their entire length, and a group of the same at the base of 

 the club. The acetabula and cushions correspond on the oppos- | 

 ing tentacles, and enable them to pull together. Other genera | 

 are Dosidicus, Todarodes, Illex, Bathyteuthis and Mastigoteuthis, * 



Fam. 6. Onychoteuthidae. — Body cylindrical, fins terminal or 

 lateral, mantle-locking apparatus elaborate, tentacular arms very 

 long, sessile or tentacular arms furnished with retractile hooks, 

 gladius lanceolate, with a terminal cone. — World-wide. 



The prehensile apparatus of Cephalopoda reaches its maxi- 

 mum of power and singularity in this family. In Onychia, Onycho- 



