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



(n 7 ) is dentate. The five teeth of the basal mouth are very unequal, two much larger 

 than the three others. The two paired gonophores together form a double body of 

 bilaterally symmetrical form. Sometimes they are of the same sex, at other times of 

 different sexes. 



Genus 15. Sphenoides, 1 Huxley, 1859. 

 Sphenoides, Huxley, Oceanic Hydrozoa, p. 61. 



Definition. — Eudoxidae with a bilateral prismatic or sphenoidal bract, bounded by 

 eight faces, twelve edges, and twelve angles. Phyllocyst composed of a large apical sac 

 and a slender odd dorsal canal descending from the base of the sac. (Eudoxise of the genus 

 Bassia. ) 



The genus Sphenoides (PI. XXXVIII.) comprises those monogastric Eudoxidas which 

 arise from the polygastric Diphyid genus Bassia (Genus 30, PI. XXXVII.). Its bract 

 has a very complicated sphenoidal form, and is distinguished by a large ovate sac of the 

 phyllocyst in the apical half of the umbrella, whilst a long slender odd dorsal canal 

 (similar to a basal spur) descends into the basal half. The original main axis of the 

 umbrella is strongly curved, so that its ventral part is shortened and its dorsal part 

 correspondingly expanded. The twelve edges of the wedge-shaped umbrella are produced 

 into twelve three-sided pyramidal teeth, five of which belong to the ventral (ii}-vF), 

 seven to the dorsal half (u c '-ii w ). The eight faces of the umbrella are four larger 

 paired lateral (a superior pair quadrangular, an inferior pair hexagonal) and four smaller 

 odd frontal faces, two superior triangular (one ventral and one dorsal) and two inferior 

 (a triangular dorsal and a hexagonal basal). The comparison of the young bract 

 (PI. XXXVIII. fig. 13) and the adult (fig. 14) exhibits the curious development of this 

 cuneiform hydrophyllium. 



The genus Sphenoides was founded by Huxley {he. cit.) upon an Australian species, 

 which he rightly suspected to be the Diphyozooid of Abyla bassensis ( = Bassia quadri- 

 latera). This species is rather different from the Atlantic species described in the 

 following, the development of which from Bassia I observed in the Canary Islands ; and 

 from another species (Sphenoides tetragond) which I observed in the Indian Ocean. A 

 fourth species may be the Eudoxia of the South Atlantic, Bassia perforata (10). 



Sphenoides obeliscus, n. sp. (PI. XXXVIII.). 



Habitat. — Northern Atlantic; Canary Islands, Lanzerote, February 1867 (Haeckel). 



Bract (fig. 12, u, lateral view from the left side, with the included parts ; figs. 13 and 

 14, lateral view from the right side; fig. 13, of a younger attached Eudoxia; fig. 14, of 



1 Sphenoides= Wedge-shaped, vtpnvoiiiris. 



