210 BULLETIN 82, UNITED STATES NATIONAL, MUSEUM. 



lateral edges gives rise to thin flange-like borders, which are usually ventrolateral, 

 in this case assisting to support the visceral mass, more rarely dorsolateral. These 

 are usually widest at the point of maximum growth activity (the distal corners) 

 and may be wholly or chiefly confined to this location. 



In general, this type of ornamentation is confined to the first brachial pairs 

 and their reduplications, or to the first two pinnule segments, biit it is occasionally 

 developed on all the brachials and pinnulars. 



In the Macrophreata production of the ventrolateral border of the ossicles 

 is very rare, but it is seen in the Atlantic species of Antedon and in species of 

 Eumetra and Imdometra and one or two other related genera. It does not occur 

 in the Comasteridfe, Zygometridfe, Himerometrid?e, Thalassometridse, Charitomet- 

 ridse, or Mariametridse. In certain species of the genera Stephanometra (figs. 125, 

 130, p. 79), Cenometra (fig. 122, p. 79, and part 1, fig. 87, p. 143), Colobometra, 

 Cyllometra, Decametra, Oligometra, and C'otylometra, as well as in some 

 forms of certain species of Lamprometra, it is usually strongly developed, taking 

 the form of broad, thin, rounded processes, usually more or less confined to the 

 distal half of the ossicles and not occurring beyond the second brachial of the 

 free undivided arms. In the Calometridse a similar condition is found, but the 

 lateral processes are more extensive and arise from a greater part of the lateral 

 borders of the segments. They often are in apposition laterally, so that the lateral 

 portion of the visceral mass is completely inclosed in a calcareous casing. 



The edges of these lateral processes, though very thin, are ordinarily entire 

 and smooth, for the deposition of calcareous matter in the crinoids in other 

 directions than that of rapid directive growth always leaves a clean, smooth edge 

 such as is seen on the posterior borders of the orals as contrasted with the opposite 

 growing angles; but in a few forms, such as C otylom-etra ornata, and the species 

 of Pectinometra, they are regularly serrate or coarsely denticulate always, how- 

 ever, with a smooth margin to the minor processes. 



In very many of the genera which have the arm bases flattened against each 

 other, especially those in which the IIBr series are 4(3+4), the whole lateral 

 border of the ossicles appears to have been pushed outward so that the ossicles are 

 sharply flattened laterally, yet when viewed dorsally appear to be strongly convex 

 dorsally with narrow, produced, and flattened borders. This is characteristic of 

 the species of Amphimetra, Heterometra, and Craspedometra of the Himeromet- 

 ridse, of Crinometra, Crossometra, Perissometra, Pachylometra, and Glyptometra 

 of the Charitometridse, of certain species of Thalassometra, and is seen in a few 

 species of Dichrometra, Liparometra, Lamprometra, and Mariametra of the Maria- 

 metridse. In (rh/ptometra the dorsolateral edges of the segments are sometimes 

 everted and stand out as a thin interradial keel. 



In Pcecilometra (figs. 118, 132, p. 79, and 229, p. 186), which has the division 

 series and arm bases close together but not quite in apposition, the dorsolateral 

 border of the ossicles has become produced, resulting in a uniform thin flange-like 

 border about the edges of the segments of the elements of the IBr series and of the 

 first brachial pairs. 



