REPORT ON THE RADIOL ARIA. 267 



Genus 109. Arachnopegma} Haeckel, 1881, Prodromus, p. 454. 



Definition. — A s t r o s p h je r i d a with five to ten or more cortical, concentric, 

 polyhedral, or spherical lattice-shells, composed of a very thin, cobweb-like network ; 

 innermost shell with hexagonal or polygonal meshes ; other shells with simj)le 

 triangular meshes, connected to one another by diagonal threads between them. 



The genus Arachnopegma difi"ers from its ancestral form, Arachnopila, in the 

 possession of peculiar diagonal threads, which connect the verticils or nodal-points of 

 every two neighbouring radial sjDines in two different neighbouring concentric shells. 

 In this case, therefore, not only do triangular meshes lie in the spherical faces of the 

 concentric spheres, but also between them, in numerous oblicpie diagonal planes ; a very 

 rare and remarkable structure, and forming a transition to spongy shells. 



1. Arachnopegma rerticiUatum, n. sp. 



Innermost shell with regular, hexagonal meshes ; its diameter is the same as the equal distance 

 between each of the two shells. Threads of the network smooth. Eadial spines twenty to forty, 

 each with fifteen to twenty verticils. 



Dimensions. — Diameter of the innermost shell O'O-l, distance between the concentric shells 0'03 

 to 0-04. 



Hcthituf. — Central Pacific, Station 266, surface. 



2. Arachnopegma longispinwn, n. sp. 



Innermost shell with regular, hexagonal meshes ; its diameter half as large as the equal 

 distance between every two shells. Threads of the network dentated or with small knots. Eadial 

 s]iines fifty to sixty, each with twenty to twenty-five verticils. 



Dimensions. — Diameter of the innermost shell 0"02 ; distance between the concentric shells 

 0-04 to 0-05. 



Hahif.at. — Central Pacific, Station 272, surface. 



3. Arachnopegma increscens, n. sp. 



Innermost shell with regular, hexagonal meshes ; its diameter quite as large as the distance 

 between it and the second shell ; only half as large as the distance between the fourth and fifth 

 shells. Forty to fifty radial spines, each with fifteen to twenty verticils. 



Dimensions. — Diameter of the innermost shell (A) 0-025 ; distance between the following 

 shells— A, E = 0-025, B, C = 003, C, D = 0-04, D, E = 0048, E, F= 0056, F, G = 0-064, &c. 



Hahitat. — Central Pacific, Station 274, .surface. 



' ^rac/inopei/ma = Cobweli-l)uil(ling ; aodx^yi, viyf/.a. 



