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



Genus 366. Phractojielta} Haeckel, 1881, Prodromus, p. 468. 



Definition. — P lir ac t op e 1 1 i d a with twenty simple radial spines, bearing no 

 free aphophyses outside the outer shell. 



The genus Phractopelta is the most simple form among the Phractopeltida, and 

 may be regarded as the common ancestral form of this family. All twenty spines are 

 of nearly equal form and size, and bear no free apophyses on their free part, outside 

 the two concentric shells. Phractopelta may be derived from Ofophaspis by further 

 development of the free apophyses, which by union of their branches form a second 

 outer shell around tlie ^jrimary shell of that Dorataspid. 



Subgenus 1. Phractopeltaris, Haeckel. 



Definition. — Outer shell composed of twenty separated plates, the sutures of their 

 meeting condyles not being grown together. 



1. Phractopelta dorataspis, n. sp. (PI. 133, fig. 1). 



Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent 

 sutures. Each plate commonly with two elliptical aspiual pores, which are two to three times as 

 broad as the irregular sutural pores. Eadial spines (in the outer free part) compressed, linear, twice 

 as long as the diameter of the shell. 



Dimensions. — Diameter of the outer shell O'll, of the inner 0'05. 



Hahitat. — North Pacific (off Japan), Station 239, surface. 



2. Phractopelta (hjadopora, n. sp. 



Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent 

 sutures. Each plate commonly with two kidney-shaped aspinal pores, which are three to four 

 times as broad as the irregular sutural pores. Eadial spines conical, about as long as the radius of 

 the shell. 



Dimensions. — Diameter of the outer shell 0'08, of the inner 0'04. 



Eabitat. — North Pacific, Station 256, surface. 



3. Phractopelta diporaspi.'i, n. sp. 



Outer shell composed of twenty j^lates, the meeting condyles of which are separated by permanent 

 sutures. Each plate commonly with two quadrangular aspinal pores, which are four to five times 



' P/irarfo2«i((i = Hedging shield ; (P^uktI;, iriMvi. 



