1350 THE VOYAGE OF H.M.S. CHALLENGER. 



45. Podocyrtis triacantha, Ehrenberg. 



Podocyrtis triacantha, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xiii. fig. 4. 



Shell conical, rough, with two di.stinct strictures. Length of the three joints = 1:2:4; breadth 

 = 2:4:6. CejDhalis hemispherical, with a very large conical horn, nearly as long as the whole 

 shell. Thorax campanulate, densely spinulate, with very small, regular, circular, quincuncial pores. 

 Thorax inflated, with very large, irregular, roundish, pores (three to four in the course of its length), 

 five to ten times as broad as those of the thorax. Feet slender and thin, subcylindrical, as long as 

 the abdomen, divergent in the proximal half, convergent and curved inwards in the distal half. 



Dimensions. - Length of the three joints, a 0-02, h 0-04, c 0-08 ; breadth, a 0-04, h 0-08, c 012. 



Habitat. — Central Pacific, Station 268, depth 2900 fathoms ; also fossil in Barbados. 



Genus 593. Thyrsocyrtis,^ Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. 



d. Wiss. Berlin, p. 54. 



Definition. — T h e o p i 1 i d a (vel Tricyrtida triradiata aperta) with three branched 

 terminal feet on the mouth of the abdomen, without lateral ribs or wings. Apex with a 

 horn, which usually bears lateral spines. 



The genus Thyrsocyrtis differs from the preceding Podocyrtis, its ancestral form, in 

 the ramification of the three terminal feet, which in the latter genus remain simple. 



1. Thyrsocyrtis rhizodon, Ehrenberg. 



Thyrsocyrtis rhizodon, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xii. fig. 1. 



Shell slender, conical, smooth, with two distinct strictures. Length of the three joints = 

 1:2:3, breadth =1:3:4. Cephabs hemispherical, with a large cylindrical horn, reaching half the 

 length of the shell, and papillate in the distal half. Pores nearly equal, regular, circular, quin- 

 cuncially disposed, small. Feet divergent, about half as long as the shell, broadened and forked at 

 the distal end. (The fork incision is often much deeper, as in the figure given by Ehrenberg.) 



Dimensions. — Length of the three joints, a G'02, h 0'04, c 0-06 ; breadth, a O'Oo, h 0-06, c O'OS. 



Habitat. — Fossil in Barbados. 



2. Tliyrsocyrtis arborescens, n. sp. (PI. 68, fig. 9). 



Shell nearly ovate, thorny, with a deep coUar, but without lumbar stricture. Length of the 

 three joints = 1:2:4, breadth = 2 : 3:4. CephaUs hemispherical, with a stout scaly or branched 

 horn, half as long as the shell. Pores irregular, roundish, small, separated by spinulated crests, 

 of slightly different sizes. Feet divergent, cylindrical, and as long as the thorax in the proximal half, 



1 Thyrsocyrtis = Basket with a thyrsus or apical rod ; ^v^uo;, xi/jtiV. 



