204 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 38. Athoralia, 1 Haeckel, 1888. 



Athoralia, Hid., System der Siphonophoren, p. 39. 



Definition. — Athoridse without a nectosac at the distal end of the bracts. Tentilla 

 with an involucre around the spiral cnidoband. Corms dioecious. 



The genus Athoralia differs from the preceding similar Athoria in three characters. 

 The rudimentary nectosac, which occupies the distal end of the bracts in the latter, is 

 wanting in the former ; the corms are dioecious ; and the cnidoband of the tentilla is not 

 naked, but enveloped by an involucrum. Athoralia, therefore, has a relation to Athoria 

 similar to that which Athorybia exhibits to Rhodophysa. A single species only, 

 Athoralia coronula, was observed by me, in December 1881, during my residence in 

 Ceylon. It was very similar to a small young Athorybia, but possessed a single siphon 

 only, with a single tentacle. Three specimens of it were captured, one male and two 

 females. The former possessed a single small gonodendron, composed of about a dozen 

 club-shaped spermaria, besides a number of young buds. Each of the two females had 

 also only a single gonodendron, composed of numerous clustered, very small gynophores, 

 each containing a single ovum. Athoralia coronula is therefore one of the rare dioecious 

 Physonectse, like Apolemia. 



Family XII. Apolemidjs, Huxley, 1859. 



Apolemidse, Huxley, Oceanic Hydrozoa, pp. 70, 127. 



Definition. — Physonectas polygastricse, with a long tubular stem of the siphosome, 

 bearing numerous siphons, palpons, and bracts, each siphon provided with a simple 

 unbranched tentacle. Nectosome biserial, with two opposite nectophores or two alternate 

 series of opposite nectophores. Pneumatophore without radial pouches. 



The family Apolemidse, founded by Huxley upon the single genus Apolemia, com- 

 prises those Physonectse which possess a biserial nectosome and a long tubular stem of 

 the siphosome, similar to the Agalmidse. They differ, however, from these latter in two 

 important points. The pneumatophore is a simple glandular invagination of the top of 

 the trunk, whilst in the Agalmidse the pericystic cavity is divided by vertical septa into 

 radial pouches. Further, the tentacles in the former are simple, not branched filaments, 

 whilst in the latter they bear a series of lateral branches or tentilla, each provided with 

 a cnidobattery. 



The first Siphonophore belonging to this family was observed in the North Atlantic 

 by Lesueur, who in 1813 executed a large and excellent picture of it, drawn and 

 engraved by himself from life. He called it Stephanomia uvifiormis (not uvaria). 

 Eschscholtz observed the same animal in the North Atlantic, and recognising it in the 



' Athoralia, derived from Athoria. 



