MONOGRAPH OF THE EXISTING CRINOIDS. 99 



In the Zygometridae (figs. 127, 136, 143, 189-191, pp. 79, 83, 109-112), as in the 

 Himerometridse, the division series and arm bases are usually in apposition lat- 

 erally with the lateral borders of the component elements sharply truncated. In 

 Catoptometra, however, they are narrow, strongly rounded, and well separated. 



In Cras-pedometra (fig. 141, p. 83), Heteromctra, Ho7naIometra, and Amphi- 

 TTietra (figs. 192, 193, pp. 115, 117) of the Himerometridse the division series and arm 

 bases are closely appressed against their neighbors and more or less extensively 

 truncated laterally; but in Hhnerometra (fig. 123, p. 79) they are narrow, strongly 

 rounded, and widely free. 



In the MariametridsB Pontiometra (figs. 139, p. 83, and 194, p. 120) has the 

 division series very narrow, very strongly rounded, and widely free laterally, while 

 in Oxymetra (fig. 195, p. 122), Liparometra. Dichrometra, and Manametra (figs. 

 129, p. 79, 196, p. 124, 197, p. 125, and 684 p. 338) they are broad and in lateral 

 contact. The latter condition is usually found in Lampromctra also, though in 

 this genus the division series, through individual variation, are sometimes narrow 

 and separated from each other. 



In the Colobometridse the conditions are very diversified; the division series 

 and first two brachials are narrow, very strongly rounded and widely separated, 

 and each of the component elements bears a broad ventrolateral flange, as in the 

 species of Stephanometridse (figs. 125, 130, p. 79), in Cenometra (part 1, fig. 87, 

 p. 143) ; they are entirely separated laterally and well rounded in Epimetra, 

 Cyllometra, Colobonietra, Decametra, Oligometra, and Prometra; and they are in 

 lateral contact in Petasometra (fig. 198, p. 127), Cotylometra (fig. 199, p. 129), 

 AustroTnetra, Ollgometrides, and Analcidometra. 



In the Calometridse (figs. 200, p. 130, 201, p. 133, 202, p. 134, and part 1, fig. 89, 

 p. 147) the postradial series are usually very narrow and widely separated, though 

 in certain cases they may be just in apposition through the broad lateral expansion 

 of the borders of the component elements. 



In the Tripiometridae (fig. 116, p. 79. and part 1, fig. 88, p. 145) the division 

 series are remarkably broad, though thin dorsoventrally, and are sharply truncated 

 laterally. 



In the Thalassometridse there is a considerable range of diversity. The ex- 

 treme of lateral flattening and of depth of rays and lower brachials is reached in 

 Asterometra (figs. 206, p. 143. 207, p. 145, and part 1, figs. 43, 44, p. 77. and 94, p. 155), 

 though, curiously enough, in the two most closely related genera, PtUomefra (fig. 

 204, p. 139, and part 1, fig. 93. p. 153) and Pterometra (fig. 208, p. 146), the elements 

 of the division series and arm bases, though broad, are very thin, so that their 

 truncated lateral borders are very narrow as in Tropiovietra. In most of the genera 

 of this family the character is well marked, but in some of the more delicate species, 

 or individuals, of Thalcmomctra (fig. 224, p. 177) and Stylomctra (figs. 124, p. 79, 

 and 219, p. 166), and in Parametra (figs. 217, p. 163, and 218, p. 164), the ossicles of 

 the division series and arm bases may be of only moderate depth, rounded dorsally 

 and laterally, and more or less separated from their neighbors. 



In the Charitometridse (figs. 226-232. pp. 180-192, 658, p. 329, 670-675, p. 335, 

 676-682, p. 338, and part 1. figs. 99, p. 160, 100, p. 162, and 101, 102, p. 163) the 



