METAZOA ECHINODERMA. 153 



times this tongue-like projection has a node on top, as in 

 fig. 3. The presence of the anus causes more or less 

 irregularity in the plates of the body (see fig. i). The 

 ambulacra run out from the mouth across the ventral disc 

 and under the oral plates to the arms. 



The arms in Haplocrinus are only slightly developed, 

 and are usually broken off in specimens, but their points 

 of attachment are seen (figs. 1-3). They consist of one 

 series of sections divided by joints, and they lie in grooves 

 which run along the sides of the orals; in two of the 

 grooves the first section of the arms is seen (fig. 3). 



Haplocrinus retains its simplicity of structure through- 

 out life, remaining "permanently in the condition of a 

 very young larva." l 



Certain peculiar specializations of structure are found 

 in Cupressocrinus abbreviatus Goldf. (No. 267), which, 

 though a primitive form, has developed, it would seem, 

 along a different line from Haplocrinus. 



This genus has a stout, round stem (PI. 268, fig. 2), 

 but according to Bather, 2 it "endeavours at times to 

 break with old traditions, and appears with a triradiate or 

 quinqueradiate stem " (see PL 268, figs. 3, 4). The body 

 is composed of a centro-dorsal plate (fig. i), made of a 

 ring of united underbasal plates. Above this plate are 

 five large basals and five radials (No. 267; also PI. 268, 

 figs. 1,2). In this genus the regularity of the plates is 

 slightly disturbed by the anal plates. The ventral disc is 

 concealed in No. 267 by the five short, simple arms which 

 are as broad at their point of attachment as the radial 

 plates (PI. 268, fig. i). These arms bore pinnules which, 

 according to Wachsrnuth and Springer, were arranged like 

 those of Blastoids, there being four or m..>re to each arm 

 joint.3 



1 Carpenter, Chall. Rep., Zool., XI, part 32, 1884, p. 157. 



2 Quart. Journ. Geol. Soc. London, Feb., 1889, p. 167. 

 3 Proc. Acad. Nat. Sci. Phila., 1886, p. 180. 



