REPORT ON THE SIPHONOPHORjE. 301 



of numerous lateral branches or tentilla. The form of the latter, and some other 



characters of organisation, exhibit some similarity with the Forskalidse (Forskaliai, 

 Pis. VIII.-X.). 



Synopsis of the Genera of Rhodalidse. 



Corona of nectophores simple. Trunk of the siphosome with a large central cavity, . . 63. Auralia. 



Corona of nectophores double or multiple. Trunk of the siphosome without large central 



cavity, ....... .... 64. Rlwdalia. 



Genus 63. Auralia, 1 Haeckel, \i 



Auralia, Hkl., System der Siphonophoren, p. 43. 



Definition. — Rkodalidae with a simple corona of nectophores, arranged in a single 

 circle. Trunk of the siphosome with a wide central cavity, surrounded by a peripheral 

 reticulum of trunk-canals. 



The genus Auralia may be regarded as the older and inferior form of Rhodalidas, 

 more closely allied to the preceding Stephalidse than the succeeding Rlwdalia. The 

 corona of nectophores is simple, as in Stephalia, and the characteristic central canal of 

 the trunk of the latter has left a remainder in the form of a wide central cavity, from 

 which the peripheral network of anastomosing trunk-canals arises. But the basal prostoma 

 (or the primary mouth) has disappeared, and the tentacles bear a series of tentilla, as in 

 Rhodalia. 



Auralia profunda, the single species of this genus which I have examined, 

 was taken in the depths of the Tropical Atlantic, and will be described after- 

 wards in my Morphology of the Siphonophorae. Its external appearance is similar to 

 that of Stephalia corona (PI. VII. fig. 39) ; but the nectophores of the simple corona 

 are more numerous and the tentacles are of the same shape as in Rhodalia (PL IV. 

 figs. 20-23). 



Perhaps belonging to this genus is another Siphonophore, from the depths of the Gulf 

 Stream (1395 fathoms), which Fewkes has described under the name Angelopsis globosa 

 (45, pt. xii. p. 972, pi. x. figs. 4, 5), and which he supposes to be a transition form 

 between the Pectyllidse and the Pneumatophorid (Physalia). The nectosome as well as 

 siphosome of this form are subglobular and of nearly equal size. The vertical section 

 (fig. 5) exhibits the flat hypocystic cavity (cav.), between the float-cavity (cav. p) and 

 the central cavity of the trunk (cav. b). The " spherical bag-like structures," which 

 Fewkes supposes to be " budding new individuals " (grm), are probably the necto- 



1 Auralia = Air-bubble of the sea, avpa, ctXia. 



