REPORT ON THE RADIOL ARIA. 701 



2. AcantJwlonche peripolar is, u. sp. (PI. 132, fig. 8). 



Two principal spines quadrangular prismatic, "with four broad prominent lamellar wings, of 

 increasing breadth towards the pyramidal distal apex. Both ends of each spine four-sided 

 pyramidal, base without leaf-cross. Two transverse and eight tropical spines about two-thirds as 

 long as the former, four-sided pyramidal in the basal half, conical in the distal half, often curved. 

 Eight polar spines very small, about one-fourth as long as the latter, short conical or pyramidal. 

 Central capsule four-sided prismatic, enveloping both principal spines. 



Dwiensions. — Length of the two principal spines 0'2, of the ten smaller spines 012, of the 

 eight rudimentary polar spines O'Oi. 



Habitat. — Central Pacific, Station 274, surface. 



Order IV. ACANTHOPHRACTA, Ricluird Hertwig, 1879. 



Acanthometrce catapliractce, Johannes Mtiller, 1858, Abhandl. d. k. Akad. d. Wiss. 



Berlin, pp. 12, 22, 49. 

 Dorataspida et Diploconida, Haeckel, 1862, Monogr. d. Eadiol., pp. 404, 412. 

 Acanthophractida, Richard Hertwig, 1879, Organismus d. Radiol., pp. 25, 137. 

 Dorataspida, Diploconida, et Sphairocapsida., Haeckel, 1881, Prodromus, p. 467. 



Definition. — Acantharia with complete latticed shell. 



The order A c a n t h o p h r a c t a, the fourth order of Radiolaria, comprises all 

 those Acantharia in which the acanthiuic skeleton is a complete latticed or 

 fenestrated shell, supported by radial spines arising from one common central point. 

 By the possession of such a complete shell the A c a n t h o p h r a c t a differ from their 

 ancestral group, the nearly allied A c a n t h o m e t r a, which represent the older and 

 simpler, first order of Acantharia. All A c a n t h o p h r a c t a are Icosacantha 

 (like the Acanthonida, their ancestral group), and possess twenty radial spines 

 disposed according to the Miillerian law (compare above, p. 717). 



Johannes Miiller, who first observed five representatives of this order, called a 

 part of them " AcanthometrcB catapliractce," and united these with the true A c a n t h o- 

 metra [Acanthometra costoto. and Acanthometra cataphracta ; Abhandl. d. k. Akad. 

 d. Wiss. Berlin, 1858, pp. 12, 49). Another part was united by him with the true 

 Haliomma {Hcdiomma echinoides, Haliomma hystrix, Haliomma tahidatiim ; 

 Abhandl. d. k. Akad. d. Wiss. Berlin, 1858, pp. 36, 37). He supposed that these 

 latter formed the immediate transition from the true Acanthometra to the true 

 Haliomma, and that their skeleton was siliceous. 



