. Bulletin - United States National Museum. Science. MONOGRAPH OF THE EXISTING CRINOIDS. 149 these spines are longest at the ventral distal corners of the pinnulars, and where the longitudinal ridge meets the distal border. In the Oligophreata there is sometimes to be observed a curious correlation between the size of, and the number of segments in, the oral pinnules and the cirri. Comanthus finguis and G. are both remarkable for the enormous size of the oral pinnules as well as for the great size, stoutness, and number of segments in the cirri, while in the allied C. solmter^ 0. tri
. Bulletin - United States National Museum. Science. MONOGRAPH OF THE EXISTING CRINOIDS. 149 these spines are longest at the ventral distal corners of the pinnulars, and where the longitudinal ridge meets the distal border. In the Oligophreata there is sometimes to be observed a curious correlation between the size of, and the number of segments in, the oral pinnules and the cirri. Comanthus finguis and G. are both remarkable for the enormous size of the oral pinnules as well as for the great size, stoutness, and number of segments in the cirri, while in the allied C. solmter^ 0. trichopetra, C. sainoana, etc., both the oral pinnules and the cirri are small and slender with comparative!}- few component ossicles. The systematic value of the oral pinnules varies very greatly in the different groups. They present reliable diagnostic characters for distinguishing the families Thalassometridse, Charitometridse, Comas- teridae, Calometridse, and Stephanometridse, and the subfamilies Ptilometrinee, Thalasso- metrinse, and Heliometrinse, and in combi- nation with the middle pinnules the family Tropiometridse. In these groups they are of relatively slight value for the differentia- tion of genera, and of still less for the dif- ferentiation of species. In the remaining families and subfamilies in which they oc- cur in widely different forms their impor- tance for the determination of genera and often of species is very great. Middle or genital pinnules. Immediately following the oral pin- nules there are usually from one to three pairs of pinnules which are more or less intermediate in character between the oral and the genital pinnules, lacking well- fig. 209.âLatebal view of type si-ecimen ob , , . T 1 1 â 1 ASTEBOUETEA LEPIDA. developed gonads and having a calcareous structure indicative of the former, though much more generalized, but possessing ambulacral grooves and nerves, lappets, and tentacles like the latter. As a rule there are two or three pairs (figs
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