532 THE VOYAGE OF H.M.S. CHALLENGEE. 



8. Hymeniastrum trigonarium, n. sp. 



Arms one and a half times as long as Ijroad, a little broader at the rounded end than at the base, 

 with three strong conical radial spines, one larger (in the radius of each arm)^and two smaller on 

 both sides of this. Patagium complete, with four to five rectilinear parallel chamber-rows, 

 enveloping the whole arms (with exception of the terminal spines) and forming a perfect equilateral 

 triangle. 



Bimoisions. — Radius of the arms (without terminal spines) O'lS ; breadth at the base O'l, at 

 the distal part 0"12. 



Habitat. — Pacific, central area. Station 268, depth 2900 fathoms. 



Genus 230. Uuchitonia,^ Ehrenberg, 1860, Monatsher. d. k. preuss. 

 Akad. d. "Wiss. Berlin, p. 831 (sensu emendato). 



Definition. — Porodiscida with three simple, undivided, chambered arms, 

 connected by a patagium ; triangular shell bilateral, one odd arm opposite to the odd 

 angle between the two paired arms. 



The genus Euchitonia, quite insufficiently characterised by Ehrenberg, was founded 

 by him (1860) for one single species, afterwards (1872) described and figured as 

 Euchitonia furcata. Retaining this species correctly as the t}q)e of this genus, I give 

 to it here the above diagnosis. In my Monograph (1862, p. 503) I described seven 

 Mediterranean species of Euchitonia. Three of these have in common the characters 

 according to the present diagnosis : Euchitonia mUlleri, Euchitonia virchoirii, Euchi- 

 tonia heckmanni ; two others a]3pertain (on account of the regular, not bilateral form) 

 to Hymeniastrum, and two others (on account of the forked, not simple arms) to 

 Trigonastrum. Afterwards (1880) three true fossil species of Euchitonia were described 

 by Stcihr (^Euchitonia cruciata, Euchitonia zittelii, and Euchitonia acuta). Some species 

 of this genus are cosmopolitan, and appertain to the most common and everywhere repre- 

 sented D i s c o i d e a. 



Subgenus 1. Stylactis, Ehrenberg, 1872 {Joe. cit.). 

 Definition. — Arms with blunt ends, without terminal spines. 



1. Euchitonia furcata, Ehrenberg. 



Euchitonia furcata, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 308 ; 

 Abbandl. d. k. Akad. d. Wiss Berlin, Taf. vi. ni. fig. 6. 



Distance between the paired arms about half as large as their distance from the odd arm. AU three 

 arms nearly of the same size and form, about twice as long as broad, one and a half times at the 



1 Euchilonia = Nice shell ; iS, xnuvia.. 



