REPORT ON THE RADIOLARIA. 289 



. Family XL ELLIPSIDA, Haeckel, 1882 (Pis. 13, 14, 39). 



Definition. P runoidea with simple ellipsoidal shell, without equatorial stricture 

 (without enclosed medullary shell) ; network a simple lattice lamella, not spongy. 

 Central capsule ellipsoidal or cylindrical, without annular equatorial constriction. 



The family Ellipsida comprises the simplest forms of Prunoidea, and 

 probably represents the ancestral forms of this whole suborder. The fenestrated shell, 

 which encloses the ellipsoidal central capsule, is a perfectly simple " cortical shell " of 

 the same form, without enclosed " medullary shell." Its form is commonly a regular 

 monaxial ellipsoid ; sometimes a little modified by unequal growth of the two poles of 

 the main axis. Two opposite large spines are often developed at these poles, or 

 it may be that instead of these, two hollow fenestrated tubes are present. 



The ellipsoidal fenestrated shell exhibits in the regular Ellipsida all the characters of 

 a geometric ellipsoid ; one main axis surpasses in length all other possible axes. All 

 sections going through this main axis are "meridian sections," with elliptical periphery; 

 all sections perpendicular to the main axis are " transverse sections," with circular 

 periphery. The largest of these is the equatorial section, which divides the main axis 

 into halves. The diameter of this equatorial plane is the " minor axis " of the ellipsoid. 



The proportion of the two axes of the ellipsoidal shell, of the major vertical or main 

 axis and the minor horizontal or equatorial axis, is commonly between 6 : 5 and 3 : 2. 

 In the former case it approaches the spherical shell, from which it is derived ; in the 

 latter case it becomes almost fusiform or cylindrical. The network of silex, constituting 

 the shell, is constantly a simple latticed lamella, never composed of concentric shells 

 (as in the Druppulida) or spongy (as in the Spongurida). The network is often very 

 regular and elegant, in other cases irregular. 



The simplest genus among the Ellipsida, and probably the common ancestral form of 

 the whole subfamily, is the genus Cenellipsis, possessing a simple ellipsoidal shell without 

 any appendages. It is derived from Cenosphcera (the simple spherical shell) by the pro- 

 longation of one axis. Cenellipsis passes over into Ellipsidium by the production of radial 

 spines on the surface (corresponding to Heliosphcera). Axellipsis is a peculiar genus 

 differing from Cenellipsis in an axial rod, which corresponds to the minor or equatorial 

 axis. In all other genera of the subfamily both poles of the main axis are distinguished 

 by peculiar polar prolongations, either hollow fenestrated tubes (as in Pipettella) or 

 strong solid spines. Both polar spines are of equal size and similar form in Ellipso- 

 xiphus, unequal in Ellipsostylus. From the latter is derived Lithapium, by reduction 

 and loss of one spine (so that only one remains) ; Lithomespilus, by production of a 

 bunch of several spines at one pole. In the three latter genera both poles of the main 

 axis are unequal, in all others equal. 



(ZOOL. CHALL. F.xr. PART XL. 1885.) Rr 37 



