REPORT ON THE RADIOLARIA. 873 



Earely the six hydrotomical or principal spines are of equal size, ami thus the 

 margin of the shell may be quite circular or regularly hexagonal (PL 139, figs. 1-3); 

 the two equatorial spines of the hydrotomical plane are usually larger than its four polar 

 spines, and thus the margin of the shell Ijecomes more or loss elliptical (PI. 139, 

 figs. 4-7). Usually (almost constantly) these six larger spines are more or less com- 

 pressed, triangular, often ver)^ broad and flat ; their two edges lie in the hydrotomical 

 plane. Their two flat surfaces are often furrowed, with longitudinal ribs or crests 

 converging towards the simple apex of the spines. 



The fourteen smaller spines are regularly disposed according to the Mlillerian law of 

 Icosacantha on both convex sides of the lenticular shell ; they are not only smaller than 

 the six principal spines, but often also of different form, much thinner and shorter, 

 sometimes needle-shaped. In the genera Hexonaspis and Hexacolpxis (PI. 139, 

 figs. 1, 2) only their inner part (inside of the shell) is developed, whilst their outer part 

 is quite rudimentary and not prominent on the surface. Therefore these genera 

 appear to possess only six marginal spines externally. 



The Lenticular Shell itself off"ers in the Hexalaspida great difficulties in the way 

 of accurate study, as its wall is constantly very thick and dark, often quite opaque and 

 non -transparent. However, prolonged accurate researches have convinced me that its 

 structure is essentially the same as in the Belonasj^ida and esjiecially in the genera 

 Dictyaspis and Coleaspis. As in these latter the twenty plates of the shell bear high 

 crests or combs on the outer surface, and by these funnel-shaped dimples are sejiarated. 

 The network of these crests is more or less regular (PL 139, iigs. 1—7). Around 

 the base of each radial spine the shell is usually elevated in the form of a conical or 

 cylindrical sheath ; the crests are prolonged into the sheaths as longitudinal ribs, parallel 

 to the spine or convergent towards its apex. Whilst in Hexalasjns and Hexonaspix 

 these basal sheaths are not at all or but little prominent (PL 139, fig. 2; PL 140, 

 fig. 16), in Hexaconus and Hexacolpus they envelop the basal half (or even more) of 

 the spines, and very often the circular or elliptical free distal edge of the sheath is 

 elegantly denticulated or serrated (PL 139, figs. 1, 3-7 ; PL 140, figs. 9—16). 



The Pores of the sheU exhibit in the Hexalaspida the same shape as in the majority 

 of the Belonaspida. Each spine bears only two broad ojjposite apophyses, the fork- 

 branches of which unite to form a polygonal shield with tvi-o pores. The number of 

 parmal pores is constantly (?) forty, as each plate possesses only two primary asj^inal 

 pores ; there are no secondary or coronal pores. The numerous (between fifty and one 

 hundred, rarely more) smaller pores between the forty parmal pores are proljably 

 always sutural pores ; however, their number and position is very difficult to determine, 

 on account of the high protecting crests ; the majority of the funnel-shaped dimjJes 

 between the latter seem to be blind, not perforated. Sometimes all the dimples, 

 except the twenty spinal ones, seem to be blind and the sutural pores appear 



(ZOOL. cdALL. EXP. — PART XL. — 1885.) Rr 110 



