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



Genus 366. Phractopelta, 1 Haeckel, 1881, Prodromus, p. 468. 



Definition. P hractopeltida 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 Orophaspis by further 

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

 outer shell around the primary 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. (PL 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 aspinal 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 Oil, of the inner O'Oo. 



Habitat. North Pacific (off Japan), Station 239, surface. 



2. Phractopelta dyadopora, 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 - 08, of the inner 0'04. 



Habitat. North Pacific, Station 256, surface. 



3. Phractopelta diporaspis, n. sp. 



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

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



1 Phractopelta = Hedging shield ; <pj*T<(?, 



