REPORT ON THE RADIOLARIA. 873 



Rarely the six hydrotomical or principal spines are of equal size, and thus the 

 margin of the shell may be quite circular or regularly hexagonal (PI. 139, fig s . i_3). 

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

 spines, and thus the margin of the shell becomes more or less elliptical (PL 139, 

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

 pressed, triangular, often very 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 Miillerian 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 Hexacolpus (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 .offers 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 Belonaspida and especially 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 separated. 

 The network of these crests is more or less regular (PI. 139, figs. 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 Hexalaspis and Hexonaspis 

 these basal sheaths are not at all or but little prominent (PI. 139, fig. 2 ; PI. 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 (PI. 139, figs. 1, 3-7 ; PI. 140, figs. 9-16). 



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

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

 branclies of which unite to form a polygonal shield with two pores. The number of 

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

 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 probably 

 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 dimples 

 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. CHAI.L. EXP. PART XL. 1885.) Rr 110 



