REPORT ON THE RADIOLARIA. 1645 



seruitubular or a half cylinder, forming a more or less prominent peristome or a 

 proboscis ; and alwaj^s in this case the open concave side of the canal -shaped groove 

 is directed towards the ventral side of the shell, the closed convex side towards the 

 dorsal side. When several teeth arise from the two lateral free margins of the groove, 

 they are also directed towards the ventral side (figs. 2, 12, 17, &c.). Often a deep 

 ventral incision or a guttural constriction separates the base of the proboscis from the 

 genuine shell. The structure of this proboscis or peristome is usually the same as in 

 the diatomaceous shell-wall ; but sometimes its lattice-work assumes a different shape. 



The opening of the mouth itself is rarely circular, usually it is elliptical or even 

 lanceolate, often triangular. Sometimes two prominent opposite lips may be distin- 

 guished as right and left, when the fissure of the mouth is prolonged in a sagittal 

 or longitudinal direction ; as upper and lower, when it is prolonged in a frontal or 

 transverse direction. The upper or dorsal lip is always more developed than the lower 

 or ventral ; and the entire semitubular proboscis may be regarded as a production of 

 the upper lip. Sometimes the latter attains an extraordinary size and development, the 

 greatest in Challenger ia murrayi (PI. 99, fig. 1). 



The teeth of the mouth, which arise fi-om the upper lip, are usually hollow, at least 

 on the base ; a prolongation of the shell-cavity arising into the base of the teeth. Their 

 form is very variable, conical, lanceolate, triangular, sabre-shaped, &c. Usually they 

 are more or less curved, and shorter than the radius of the shell ; rarely they are straight, 

 and longer than the radius (PL 99, figs. 5, 6). More important is their different 

 number, which we have employed for the distinction of subgenera ; future observations 

 may prove that they are different genera. The most important are the following cases : 

 — (A.) a single odd dorsal tooth (figs. 5, 16) ; (B.) two paired lateral teeth (figs. 4, 6, 17) ; 

 (C.) three teeth, an odd dorsal and two paired lateral (figs. 7, 9, 10) ; (D.) four paired 

 teeth, two dorsal and two ventral (figs. 3, 13); (E.) five teeth, an odd dorsal and two 

 pairs of lateral (figs. 2, 12) ; (F.) six teeth in three lateral pairs (fig. 1). 



The teeth of the peristome are not the only apophyses which arise from the shell of 

 the ChallenD-erida. In the majority other spines appear on the sagittal margin, which 

 separates the right and left halves of the shell. These marginal spines are characteristic 

 of the genera Challengeron and Porcupinia ; they are usually radially directed, straight, 

 conical, sometimes solid, at other times hollow. Their number and arrangement is veiy 

 variable and serves for the distinction of species ; the following differences are the most 

 important : — (A.) a single odd spine on the apical pole of the shell, in the principal axis, 

 opposite to the centre of the mouth (PL 99, figs. 6, 7); (B.) two aboral spines, a dorsal 

 and a ventral (figs. 8-10) ; (C.) a bunch or a crowded group of radial spines on the 

 aboral marp-in of the shell, usually one larger apical spine surrounded by several smaller 

 dorsal and ventral (figs. 11, 12, 16) ; (D.) numerous radial spines along the whole sagittal 

 margin of the shell (figs. 13-15). 



