372 



PART II. SYSTEMATIC ACCOUNT 



generally more or less cylindrical (Fig. 149 A, 2?, C, Z)), but in one specimen 

 the front half was found to be considerably narrower than the back half, 



probably as a result of unequal contraction 

 of the musculature. It is always perceptibly 

 flattened dorso-ventrally. A very distinct, 

 straight, annular groove, dividing the proto- 

 soma from the mesosoma, is situated a little 

 in front of the bridle (Fig. 149 А, В, C, D). 

 In many specimens, moreover, it is possible to 

 observe a more or less evident post-tentacular 

 groove (Fig. 149/)). The large, pointed ce- 

 phalic lobe is roughly triangular and slightly 

 flattened. The very long tentacles are 

 attached symmetrically, close together (Fig. 

 148Л, 149Л, В, C, D). They may be equal, 

 or in a few individuals the left is a little thin- 

 ner than the right (Fig. 149Z)). The very fine, 

 delicate pinnules are arranged in two rows 

 close together on each tentacle (Fig. 148Z?), 

 except on the basal part, where they are ab- 

 sent. The rather stout, almost colourless 

 keels of the bridle, which is situated in the 

 front part of the mesosoma, lie on weakly 

 developed cutaneous ridges and are fused 

 neither dorsally nor ventrally (Fig. 149 A, B). 

 Each consists of a basal axis, tapering towards 

 both ends, and a row of cuticular rodlets fit- 

 ting close behind (Fig. \49E). The latter are 

 developed only along the ventral half of the 

 bridle. The hind end of the mesosoma is 

 rounded and slanting in side view, so that on 

 the dorsal side the mesosoma is a little longer 

 than on the ventral side. The groove dividing 

 it from the metasoma is very sharp, particu- 

 larly on the dorsal side. Sometimes a very 

 weakly marked mid-dorsal furrow may be de- 

 tected behind the bridle. 



The first part of the metasoma bears be- 

 tween 18 and 32 pairs of densely packed, 



Fig. 148. Diplobrachia japonic a: 

 A - the front end of the body from 

 the left side (the distal part of one 

 of the tentacles is missing); В - 

 part of a tentacle. 

 с - cephalic lobe;/- bridle; ms - 

 mesosoma; mts - metasoma; pi - 

 pinnules; ps - protosoma; t - 

 tentacle. 



