1208 THE VOYAGE OF H.M.S. CHALLENGER. 



14. Lithomelissa decacantha, n. sp. (PI. 56, fig. 2). 



Sethomelissa decacantha, Haeckel, 1881, Prodromus et Atlas. 



Shell smooth, with deep collar stricture, and with ten prismatic spines of nearly equal size 

 and similar form. Eelative length and breadth of the two joints about equal. Cephalis ovate, in 

 the upper half hyalme, in the lower half with few scattered pores ; in the equator with four 

 prismatic horns of the same length, which diverge upwards ; three of them are placed in the same 

 meridional planes as the three wings and the three feet of the thorax (one occipital and two 

 parietal); the fourth (frontal) horn is opposed to the occipital. Thorax campanulate, three-edged, 

 with three vertical prominent feet (directed downward) and three horizontal wings, arising from 

 their knees. Mouth wide open, not constricted. 



Dimensions. — CephaUs 0'05 diameter ; thorax 0-05 long, 0'06 broad. 



Habitat. — Equatorial Atlantic, Station 347, surface. 



Genus 538. Psilomelissa,^ Haeckel, 1881, Prodromus, p. 431. 



Definition. — Sethopilida (vel Dicyrtida triradiata aperta) with three free 

 lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. 

 Cephalis smooth, without a horn. 



The genus Psilomclissa has the same formation of the shell as the nearly allied 

 preceding genus Lithomelissa, and may be derived from it by reduction and loss of the 

 cephalic horn. The cephalis is quite bare. 



1. Psilomelissa galeata, Haeckel. 



Dictyoeeplialtts galeatus, Ehrenberg, 1872, Aljhandl. d. k. Akad. d. Wiss. Barlin, p. 289, Taf. vii. 

 fig. 25. 



Shell smooth, with sharp collar stricture. Eelative length of the two joints = 5:3, breadth =4:5. 

 Cephalis ovate, with numerous irregular, roundish pores. Thorax truncate, conical, with a few small 

 pores. From its upper part (below the collar stricture) there arise three thin, bristle-shaped, 

 widely divergent wings, about as long as the cephalis. Mouth widely open. 



Dimensions. — Cephalis 0'05 long, 0'04 broad ; thorax O'OS long, 0'05 broad. 



Habitat. — Western Tropical Pacific, Stations 200 to 225, surface. 



2. Psilomelissa phalacra, n. sp. 



Shell smooth, with deep coUar stricture. Eelative length of the two joints = 5:6, breadth = 4:4. 

 Cephalis ovate, hyaline, with few small pores only in the lower third. Thorax cylindrical, truncate, 

 with small irregular, roundish pores. From its upper third there arise below the stricture three club- 



' Psilomelissa = Smootli bee ; •^I'Koi, /ii^icaa. 



