REPORT ON THE RADIOLAEIA. 765 



meet together, tlieu the characteristic lattice-shell of the Tesseraspida is perfect. 

 Either each plate bears four crossed pores (like Tesseraspis), or a larger number 

 of pores (four aspinal and four to eiglit or more coronal) like Icosaspis. 



1. Phatnacantha tessaraspis, n. sp. 



Spines quadrangular prismatic, witli simple pyramidal apex and small basal leaf-cross. Each 

 spine bears in the basal half a square plate, which is perforated by four square pores ; margin of 

 the plate with twelve short straight teeth. 



Dimensions. — Length of the spines 012, breadth 0'005. 



Habitat. — Central Pacific, Station 265, surface. 



2. Phatnacantha icosaspis, n. sp. (PL 130, fig. 6). 



Spines quadrangular, with prominent edges ; prismatic in the basal half, with a broad basal 

 leaf-cross, pyramidal in the distal half, with a simple or truncate apex. Each spine bears in the 

 middle part a square plate, which is perforated by eight to sixteen or more square pores (four 

 aspinal and four to eight or more coronal) ; margin of the plate with twenty-four to forty-eight 

 or more short straight irregular compressed teeth. 



Bimerisions. — Length of the spines 018, breadth O'OOS. 



Habitat. — Central Pacific, Station 27?>, surface. 



Genus 333. Pristacantha,^ n. gen. 



Definition. — A s t r o 1 o n c h id a with numerous simple apophj'^ses (eight to 

 sixteen or more on each radial spine) which are arranged in four longitudinal rows 

 opposite in pairs in the form of a cross. 



The genus Pristacantha differs from all other Stauracanthida in the multiplica- 

 tion of the crossed apophyses (at least eight on each spine), and exhibits therefore to 

 them the same relation as Astrolonche exhibits to the other Phractacanthida. The 

 remarkable Astrolonchidivm serratum appears intermediate between both groups. 



1. Pristacantha octodon, n. sp. (PL 130, fig. 9). 



Spines four-sided prismatic, a little broader in the middle part than at either end, with thin 

 prominent edges. Apex truncate or pyramidal. Base pyramidal, with a small leaf-cross. From 

 the four edges arise in the basal half (between first and second third of the length) eight slender, 

 conical, or triangular apophyses (two on each edge). 



Dimensions. — Length of the spines 0'4 to 0'6, breadth 0"02 to 0'04. 



Habitat. — Central Pacific, Station 271, surface. 



' Pn's(acani/io = Saw-spine ; t^ihto;, dxicvdn. 



