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



and its single tentacle into a palpacle. Beyond these sterile medusomes have been 

 developed the fertile ones, in the form of gonostyles, which have produced by budding 

 the gonodendra composed of numerous Medusoid gonophores. 



Genus 36. Circalia, 1 Haeckel, 1888. 

 Circalia, Hkl., System der Siphonophoren, p. 38. 



Definition. — Cirealidse with a single corona of nectophores radially arranged around 

 the pneumatophore, and with a series of simple filiform tentilla on the single tentacle. 



The genus Circalia (PI. XXI. figs. 1-4), as the single known genus of Circalidfe, 

 possesses the characters of the famdy described above. As a peculiar character of the 

 genus may be pointed out the remarkable composition of the corona of (eight) radial 

 nectophores, similar to that of Stephalia (PI. VII. figs. 39, 48). Another character of 

 generic value may be the simple tubular shape of the tentilla, or the filiform lateral 

 branches of the single tentacle (similar to Nectophysa wyvillei, PI. XXIII. fig. 5). It 

 differs in this from the similar Circonalia haplorhiza ( = Physophora alba, Quoy and 

 Gaimard, 2). Compare above, p. 197. 



Circalia stephanoma, n. sp. (PL XXI. figs. 1-4). 



Habitat. — North Atlantic, west coast of Norway, near the Sogne Fjord ; September 

 1869 (Haeckel). 



Nectosome. — The swimming apparatus has a diameter of about 5 mm., and is composed 

 of a large apical pneumatophore and a corona of eight nectophores radially arranged 

 around it. These are attached by short ventral pedicles to a central axial trunk, the 

 uppermost dilated part of which is the pneumatophore, whilst the lower part of the 

 trunk passes over directly into the base of the siphon. From the dorsal side of the latter 

 arises the single tentacle, whilst in the median line of the opposite ventral side (between 

 the two ventral nectophores) a small group of young buds is visible. 



Pneumatophore. — The float at the apex of the trunk is pyriform or subspherical, 

 of about the same size as the nectophores (2 or 3 mm. in diameter). Its apex bears 

 a ventral depression or umbilicus (perhaps the closed opening ?) and around this a red- 

 brown pigment-star, composed of eight equidistant triangular rays. The basal half exhibits 

 eight longitudinal grooves, the insertions of the radial septa which divide the cavity of 

 the pneumatophore into eight radial pouches (fig. 4, pq, in horizontal transverse section). 



Nectophores (figs. 1, 2, n). — The eight swimming-bells which compose the octoradial 

 corona around the central pneumatophore are of rather regular campanulate form. 



1 Circalia = Marine corona, x/pxo;, aTiioj. 



