•202 THE VOYAGE OF H.M.S. CHALLENGER. 



Athoria larvalis, n. sp. (PI. XXI. figs. 5-8). 



Habitat. — Indian Ocean; Belligemma, Ceylon, December 1881 (Haeckel). 



Nectosome. — The swimming apparatus is composed of an apical pneumatophore and 

 a corona of fifteen to twenty large bracts ; these are attached by the pointed end of a 

 pyramidal pedicle to the axial trunk, immediately below the base of the float. They are 

 raised and lowered by special muscles in the same manner as in the similar Antho- 

 physidaa. The thick bracts are therefore not only protective but also paddling organs, 

 as in Athorybia. The diameter of the entire nectosome is 5 to 6 mm. 



Pneumatophore (figs. 5, 6, p). — The apical float is of medium size, pyriform. with 

 rounded top and dilated basal part. The latter is divided by a horizontal annular 

 constriction (or pneumatic pylorus) into an upper and a lower cavity ; the greenish 

 epithelium of the latter is the pneumadenia. A chitinous pneumatocyst (fig. 6, p>f) w as 

 recognisable in the upper part. The pericystal cavity of the pneumatophore (pc) is 

 simple, without radial septa ; similar to that of the Apolemidse. 



Bracts (figs. 5, 6, b). — The large hydrophyllia are five-sided, prismatic, with five 

 prominent convex edges, about three times as long as thick. An odd superior or dorsal 

 edge, and the two parallel dorso-lateral edges are elegantly denticulate, whilst the two 

 inferior or ventro-lateral edges are smooth. The ventral or axial face between the last 

 is concave. The proximal fourth of the bract is a five-sided irregular pyramid and its 

 apex prolonged into the short pedicle, which attaches the hydrophyllium to the trunk. 

 The distal third is oblicmely truncated and contains a small hemispherical or campanulate 

 cavity (fig. 6, bs). This is the rudimentary subumbrella, the muscular nectosac of which 

 is preserved. The simple bracteal canal (be) which enters by the pedicle, runs along the 

 middle line of the concave ventral face and touches the top of the subumbrella ; four very 

 small radial canals (cr) seem to arise from it, run along the nectosac towards its small 

 distal ostium, and are there connected by a small ring-canal. The four equidistant points, 

 where they open into the ring, are armed with a small cnidonode (k), which is composed 

 of four cnidocysts (rudiments of lost tentacles ?). 



Siphosome. — The inferior part of the corm, beyond the superior corona of bracts, is 

 composed of a large central siphon and a corona of palpons which surrounds its proximal 

 base. From this arises a long tentacle, beset with a series of tentilla. Each palpon bears 

 at its base a simple palpacle. A pair of gonostyles is attached on each side of the trunk 

 of the siphonal pedicle, between the palpons and the basigaster. The male gonophore 

 lies on the left and the female on the right side of the siphon, whilst the insertion of the 

 tentacle occupies the middle of the dorsal side of its base, and a small group of buds 

 the middle line of its ventral side. The frontal section in fig. G, which exhibits these 

 topographic relations, is semi-diagrammatic. 



