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



the Tropical and Subtropical Atlantic, and was collected by the Challenger at Stations 

 338 and 346. In 1867 I had observed the same species living, during my stay in the 

 Canary Island, Lanzerote. A comparison of its form (PI. XXXIX.) with the figures of 

 the Mediterranean Calpe pentagona exhibits, at first sight, the important differences 

 between the two species. A third species, different from both, is the inhabitant of the 

 Tropical Pacific and Indian Ocean, figured by Huxley in his excellent work also as 

 Abyla pentagona (9, pi. ii. fig. 2). I name it in honour of this naturalist, so highly 

 respected for his additions to our knowledge of the Acalephs, Calpe huxleyi. 



Calpe gegenbauri, n. sp. (Pis. XXXIX., XL.). 



Habitat.— Tropical and Southern Atlantic ; Station 338, March 21, 1876; lat. 21° 15' 

 S., long. 14° 2' W. 



Station 346, April 6, 1876 ; lat. 2° 42' S., long. 14° 41' W. Surface. 

 Canary Islands, Lanzerote, February 1867 (Haeckel). 



Nectophores. — The two nectocalyces united are 24 to 28 mm. long ; they are very 

 different in form and size. The posterior or distal nectophore is 20 to 22 mm. long and 

 9 to 10 mm. broad; it is twice as broad and four times as long as the anterior or 

 proximal, whose length is 5 to 6 mm., and the breadth 4 to 5 mm. The ground-form 

 of the larger is very asymmetrical, that of the smaller quite symmetrical. 



Apical Nectophore (figs. 1-4, cs ; fig. 5, apical view; fig. 6, dorsal view; fig. 7, 

 ventral view ; fig. 8, lateral view from the left side). — The first nectophore (also called 

 the proximal, anterior, superior or apical nectocalyx) is a pentagonal prism of a com- 

 pletely bilaterally symmetrical ground-form. When the axis of its nectosac stands 

 vertically, then the two pentagonal and parallel terminal faces of the prism are also 

 vertical, and one of their five angles (opposed to the basal side) is directed upwards ; the 

 two odd apical angles being connected by the horizontal coryphal crest (figs. 5-8, nk). 



The pentagonal dorsal face of the first nectophore (fig. 6, ud) covers the nectosac (iv), 

 and is much smaller than the similar ventral face (fig. 7, iiv), through which the soma- 

 tocyst (cs) appears, and beyond it the hydrcecium (ui). The two superior lateral angles 

 of each pentagonal terminal face are much more distant than the two inferior ; and the 

 lines connecting the two angles at each side (the inferior lateral edges of each pentagon) 

 are turned inwards, and form an obtuse angle. 



The five lateral faces of the pentagonal prism, which separate its two parallel terminal 

 faces (dorsal and ventral) are two pairs of lateral faces (superior and inferior), and an odd 

 inferior or basal face (with the openings of the dorsal nectosac and the ventral hydrcecium). 



The two paired sujiero-lateral faces of the first nectophore are quadrangular, nearly 

 rectangular, and connected in the sagittal axis of the body by the coryphal crest (nk) ; 



