REPORT ON THE RADIOLARIA. 1731 



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four separate tubes or four pairs of tubes arise from each galea, viz., two from the two 

 anterior corners of the basal triangle, one from the posterior corner, and one from the 

 apex of the galea. It is possible that this difference in the origin, furcation, and number 

 of the hollow radial tubes may be employed for the distinction of genera of Coaloden- 

 drida, in the same manner as it is employed in the next following family, the 

 Coelographida. But I have not been able, in spite of numerous and accurate examina- 

 tions, to demonstrate in the former the same regularity in number and arrangement 

 of the tubes as in the latter. It seems that these relations here are very variable, even 

 in one and the same species, and not yet fixed. 



It is, however, probable, on the other hand, that the primary tubes (all or partly) 

 are identical in the Ccelodendrida and Coelographida. This is most probably the case 

 with the posterior odd or caudal tube, which seems to be never wanting, and in both 

 families is developed in the form of a dichotomous brush (never in the form of a verticillate 

 style). Possibly also the two paired pectoral tubes are homologous in both families. 



The hollow tubes are perfectly simple and unbranched only in one genus, 

 Ccelodoras, which is probably the common ancestral form of both families, and 

 which may have been derived from Concharium by development of a galea and tubes 

 on the sagittal apex of the valves. All the other Coelodendrida have branched spines, 

 and the ramification is constantly dichotomous, or repeatedly forked. There never 

 occur in this family those characteristic " styles," or verticillate prolonged tubes, which 

 we find in all Ccelographida. Usually the cylindrical tubes are slightly curved and 

 forked even near their base. The furcation is repeated a variable number of times in the 

 different species. In the largest species each tube becomes a brush with more than one 

 hundred terminal bristles. 



We divide the Coelodendrida into two subfamilies, according to the different 

 development of the distal branches of the hollow tubes. In the Coelodorida all the 

 branches of the tubes remain free and are never connected by anastomoses, so that the 

 surface of the bivalved skeleton is protected by the free radial distal branches of the 

 tubes. In the larger species of Ccelodendrum (e.g., Ccelodendrum furcatissimum, 

 PL 121, fig. 1), the numerous branches of the dichotomous tubes form a dense thicket, 

 similar to that in the Coelotholida. 



In the second subfamily, Coelodrymida, the distal branches of the tubes are 

 connected by numerous anastomoses, and compose either a simple lattice-plate on the 

 surface of the skeleton (Ccelodrymus), or a thicker envelope of spongy framework 

 (Caslodasea). The lattice-mantle so produced is always bivalved, and its two outer 

 hemispherical valves (dorsal and ventral) correspond exactly to the two inner 

 valves, from which arise the hollow tubes. The free margins of the two external 

 mantle-valves come externally into contact in the equatorial plane of the body, in which 

 the girdle-fissure lies internally between the two central shell-valves. The free edges 



