SYSTEMATIC AND BIOLOGICAL ACCOUNT 155 



and measures 23 mm. in length, the smaller, male, 20 mm. They fit accurately together, as shown in 

 Text-fig. 81, the hydroecial wings of the larger clasping those of the smaller at the upper and lower 

 sides of the whole eudoxid. The pedicular canals of the two gonophores arise near the forward end 

 on the borders of their upper hydroecial wings, so that they must arise just below the forward end 

 of the swan-shaped somatocyst 1 . In fact, scars of corresponding shape can be seen in this position 

 on the bract. The hydroecial wings of the gonophores surround the gastrozooid and its tentacle. 

 This combined hydroecial cavity narrows towards its after end, and at its periphery there are two 

 large curved teeth, one above the other, and one belonging to each gonophore. These large teeth are 

 in positions about two-thirds of the way down the obliquely running hydroecial folds, which bear 

 a few more much smaller distal teeth. Such teeth are commonly found on the hydroecial fold or 

 'Leiste' of gonophores and of posterior nectophores of many genera and species. In the posterior 

 nectophore of this species dentata there are about two dozen teeth on the left hydroecial fold, the ter- 

 minal one as usual being the largest. Their function perhaps is to prevent entanglement of the 

 numerous side branches of the tentacles, or to remove prey. 



In structure the gonophores of Ceratocymba dentata are perhaps more complicated than those of 

 any other species of Siphonophore, a fact that strengthens the belief that it is the most highly evolved 

 Calycophore. 



Abylopsinae 

 Abylopsis tetragona (Otto), 1823. 



In 1 95 1, nine open hauls containing Siphonophores were made by ' Manihine ', six of them during 

 the night of 16-17 January between five miles and forty miles east of Sanganab Lighthouse, off Port 

 Sudan, from either 183 or 366 m. to the surface. An examination of the catches showed that 

 A. tetragona was abundant and actively breeding. At three other 'Manihine' Stations 1 (P), 2 and 3, 

 further north, fifty-six polygastric specimens, and 276 eudoxids were taken. 



_ - Som. 



Nsobs 



Tov.r 



Whydr Whydl Cmb 



Text-fig. 82. Abylopsis tetragona. The two nectophores locked rigidly together as in life. 



Xf2. 



Since the ' Manihine ' catches appear to be some of the first records of Siphonophores from the 

 Red Sea it was thought worth while to compare the absolute abundance per unit volume of water of 

 this species in the Red Sea ('Manihine' records), in the Mediterranean ('Thor' records) and in the 

 warm tropical Atlantic ('Meteor' records). Bigelow & Sears (1937) went into the question of the 

 last two in some detail. Here I need only give the comparable figures and repeat the caution about 

 accepting figures based on a small number of open hauls, where the straining efficiency of the net, the 



1 Clearly shown in Text -fig. 80. 



