REPOET ON THE RADIOLARIA. 999 



basal gates ; two others are prolongations of the sagittal ring (sternal and caudal), and arise from the 

 medial corners of the basal gates. (Tiie shell is like a small cube with four feet.) 



Dimaisions. — Length of the shell 013, breadth Oil. 



HaUtat. — North Pacific, Station 253, depth 3125 fathoms. 



5. Microcuhns cornutus, n. sp. 



Eight gates (two mitral, two basal, and four superior) simple ; four inferior gates fenestrated by 

 arachnoidal irregular threads. Frontal ring square, constricted on the sides by the equatorial ring. 

 Basal ring with four short conical vertical feet, as in the preceding species. Sagittal ring with a 

 vertical horn on the apex. All rings with small scattered thorns. 



Dimc7isions. — Length of the shell Oil, breadth 013. 



Habitat. — North Pacific, Station 235, surface. 



6. Microcubus ampliisjiyris, n. sp. (PL 94, fig. 10). 



Four gates (two mitral and two basal) simple ; eight lateral gates (four superior and four 

 inferior) fenestrated by arachnoidal u-regular threads. Frontal ring convex, not constricted by the 

 equatorial ring. Basal ring with six short conical divergent feet (two sagittal and four lateral). 

 Sagittal ring with an apical horn. (Resembles some S p y r o i d e a.) 



Dimensions. — Length of the shell 0'08, breadth 012. 



Habitat. — Central Pacific, Station 272, depth 2600 fathoms. 



Genus 429. Octotympanum,^ n. gen. 



Definition. — T ympanida with two bisected horizontal rings converging laterally 

 and connected in the lateral poles of the equatorial plane. Eight large gates. 



The genus Octotijmpanum differs from all other Tympanida in the peculiar connection 

 of the tw^o horizontal rings, which here reach the maximum of their growi;h, converge 

 towards the equator, and come into direct contact on the poles of the equatorial trans- 

 verse axis. Therefore the shell appears to be composed of three complete vertical 

 meridian rings, the middle of which (the sagittal ring) is free and simple ; the two 

 other (subfrontal) rings are grown together at the lateral poles of the equatorial plane ; 

 commonly at these poles there arises (on the right and left) a strong lateral spine, and 

 the base of this (or the crossing point of the two touching horizontal rings) corresponds 

 to the remnants of the shortened frontal ring. The crowm-shaped shell exhibits there- 

 fore eight large gates ; two superior (mitral) and two inferior basal gates, two larger 

 anterior (facial) and two larger posterior (occipital) gates. Seen from the lateral jDoles 



' Octot'ympanum='[)n\m with eight gates; mzu, Ti/|Kx«>of. 



