1368 THE VOYAGE OF H.M.S. CHALLENGER. 



of half the breadth, with larger hexagonal meshes. Thorax and abdomen pierced by four stout 

 radial ribs, lying opposite in pairs in two diameters, perpendicular one to another. No secondary or 

 interradial ribs are interpolated between the four primary. Mouth truncate, circular. 



Dimensions. Length of the three joints, a 0'02, 5 0'08, c 0'04 ; breadth, a 0'05, I 018, c 0'25. 



Habitat. Central Pacific, Station 274, surface. 



4. Theophormis senaria, n. sp. 



Shell flat, hat-shaped, similar to Theophormis callipilium (PI. 70, figs. 1-3), but with a different 

 number and arrangement of the piercing radial ribs. The cephalis and its collar septum exhibit the 

 same formation as in Sethophormis hexalactis, described above (p. 1245, PI. 56, fig. 6.) The caudal 

 and sternal ribs, which are opposed in the sagittal plane, are simple, whilst the two lateral ribs are 

 forked. In the flat abdomen there are six secondary or interradial ribs, interpolated between the six 

 primary or perradial ribs of the thorax. Delicate network with regular, hexagonal meshes. 



Dimensions. Length of the three joints, a 0'035, & 0'075, c O025 ; breadth, a 0'07, 0'2, c 0'3. 



Habitat. Central Pacific, Station 272, surface. 



Genus 602. Phormocyrtis, 1 n. gen. 



Definition. T heophormida (vel Tricyrtida multiradiata aperta) with numerous 

 radial ribs enclosed in the wall of the thorax, and of the ovate or cylindrical abdomen ; 

 mouth of the latter constricted. 



The genus Phormocyrtis differs from the preceding Theophormis in the ovate or 

 cylindrical form of the abdomen, the mouth of which is more or less constricted. The 

 former exhibits, therefore, the same relation to the latter that Sethamphora bears to 

 Sethophormis among the Dicyrtida. Phormocyrtis may be derived directly either 

 from Sethamphora by development of an abdomen, or from Pterocorys or Theopilium 

 by multiplication of the three radial ribs. 



1. Phormocyrtis carinata, n. sp. 



Shell ovate, with two slight strictures. Length of the three joints = 1:2:3, breadth = 1:3:4. 

 Cephalis hemispherical, with a stout pyramidal horn of twice the length, and few very small 

 pores. Pores in the campanulate thorax and the inflated abdomen regular, circular, small, and 

 numerous. Six stout prominent ribs, beginning from the collar stricture, arise along the thorax 

 and abdomen, and reach the constricted mouth, which is half as broad as the abdomen. (This 

 species is very similar to Pterocorys carinata, from which it differs in the six complete radial ribs of 

 the shell-wall.) 



Dimensions. Length of the three joints, a 0'03, & 0'06, c 0'09 ; breadth, a 0'03, I 0'09, c 012. 



Halitat. Tropical Atlantic, Station 347, depth 2250 fathoms. 



1 Phormocyrtis = Plaited basket; 



