REPORT ON THE SIPHONOPHOR^E. 123 



Erssea, as the monogastric generation of Diphyopsis, differs essentially from Gucullus 

 as the free Eudoxia of Diphyes. The latter never possesses the individual " special 

 nectophore," which is characteristic of the former. This swimming organ must be 

 regarded as the first sterile gonophore, which has lost the manubrium, the muscle-plate 

 of the subumbrella being the more strongly developed. 



Erssea compressa, n. sp. (PL XXXIV.). 



Habitat. — Tropical and Subtropical Atlantic; Stations, 348, 349, 352, 353, &c. 

 Canary Islands, Lanzerote, December 1866 and January 1867 (Haeckel). 



Bract (figs. 9, 10, 11, b). — The hydrophyll or bract is in general irregularly conical 

 or campanulate, with a deep fissure along the truncate ventral side ; the broad basal or 

 inferior aperture is also obliquely truncate. An annular collar constriction, corresponding 

 to that part of the umbrella wdiich was attached to the stem of Diphyopsis, divides the 

 bract into a smaller apical (proximal or superior) part (fig. 11, bs) and a larger basal 

 (distal or inferior) part. The latter encloses the siphon and its tentacle, and partly 

 the gonophores, like a mantle, while the former is comparable to the cowl of the mantle. 

 This cowl contains in its solid dorsal half the phyllocyst (cs), with a central cavity 

 and a globular oleocyst on the apex (co) ; its ventral half is excavated and originally 

 embraces the stem of siphosome (fig. 9, a) ; the two ventral wings of this cavity overlap one 

 another in the middle part. The length of the bract is 6 to 8 mm., its breadth 3 to 4 mm. 



The campanulate mantle, or the larger distal half of the bract, exhibits around its 

 wide basal opening four acute triangular teeth, comparable to the four corners of the 

 original medusa-umbrella. The pair of dorsal teeth is larger and more prominent than 

 the pair of ventral teeth. The two opposite free ventral margins of the bract are 

 smooth. 



SipJion (figs. 9, s, 10, s, 11, s). — The polypite or siphon occupies originally the axial 

 part of the bracteal cavity, between the dorsal tentacle (t) and the ventral nectophore 

 (nn). The basigaster (sb) is separated by a sharp pyloric constriction from the stomach, 

 the wall of which exhibits eight longitudinal hepatic ridges. The mouth of the muscular 

 proboscis is surrounded by sixteen short lobes (so). 



Tentacle (figs. 9, t, 10, t, 11, t). — The long cylindrical tentacle is distinctly articulated, 

 and from the constriction between every two segments arises a thin tentillnm or secondary 

 filament (fig. 18). The terminal filament of the latter (tf) is about as long as its pedicle 

 (ts). The ovate cnidosac placed between them exhibits on its convex side six to eight 

 longitudinal rows of small medial cnidocysts (km), on its base two paired groups of 

 large lateral cnidocysts (six to eight spindle-shaped cnidocysts, kg, in each), and at the 

 distal part a trilobate group of pyriform cnidocysts (kp). 



