1420 THE VOYAGE OF H.M.S. CHALLENGER. 



of pores, which are twice to four times as large as those of the thorax. Mouth truncated, with 

 thickened margin, two-thirds as broad as the abdomen. 



Dimensions. — Length of the three joints, a 0-04, h 0-12, c 0-16; breadth, a 0-04, h 016, c 02. 



Habitat— Genixdl Pacific, Station 268, depth 2900 fathoms. 



Genus 620. Axocorys,^ Haeckel, 1881, Prodromus, p. 434. 



Definition. — Theocorida (vel Tricyrtida eradiata aperta), with ovate abdomen, 

 including an internal vertical axial rod, which bears three divergent radial spines or 

 verticUs of three branches, and is prolonged into an apical horn. 



The genus Axocorys contains only a single but very remarkable species, and may, 

 perhaps, represent a peculiar group, which has closer relations to the Plectoidea than 

 to the other Tricyrtida. The pyriform three-jointed shell has neither lateral nor 

 terminal free appendages, but possesses a very large apical horn, and an inner pro- 

 longation of this, an axial rod, which bears some triradiate verticds of branched spines. 

 The original ancestral forms of this remarkable genus are probably Plagoniscus and 

 Plectaniscus (pp. 912 and 924). 



1. Axocorys macroceros, n. sp. (PL 68, figs. 1, la). 



Shell pear-shaped, with two distinct strictures. Length of the three joints = 2 : 3 : 16, breadth 

 = 3:6:16. Cephalis hemispherical, with few small pores. From its apex arises vertically a 

 very long three-sided prismatic horn with denticulate edges, three to four times as long as the 

 shell. An inner thin prolongation of the horn descends vertically nearly to the mouth, and bears 

 on its basal end three verticils of branched spines, each verticil with three divergent forked spines 

 (fig. 1«). Pores regular, circular, in the subspherical abdomen three times as large as in the hemi- 

 spherical thorax. The constricted mouth is scarcely broader than the thorax. 



Dimensions. — Length of the three joints, a 0-02, b O'OS, c 0-16 ; breadth a 0-03, h 0-06, c 016. 



Habitat. — Central Pacific, Station 271, depth 2425 fathoms. 



Genus 621. Lophocorys,' Haeckel, 1881, Prodromus, p. 434. 



Definition. — T heocorida (vel Tricyrtida eradiata aperta), with ovate abdomen, 

 broader than the constricted mouth. Cephalis with two divergent horns, or with a 

 bunch of horns. 



' .4a;oco?'i/s = Helmet with an internal axis; eZfis, xo'^t/f. 

 ^ Zioy/iocorj/s — Helmet with a top crest; y^o(pos, xi^vs- 



