C. Wachsmuth—Structure of Paleozoie Crinoids. 187 
other by anal plates or by the proboscis. These seven pieces 
which i will call the “apical plates,” are easily recognized by 
their greater prominence and size in species with comparatively 
few summit plates and a lateral anal aperture; but their identi- 
fication is more difficult in species in which a subcentral pro- 
boscis is placed between the two small plates, and the whole 
vault looks like an immense proboscis. In these forms, the 
four large plates, together with the two smaller ones, are pushed 
toward the anterior side of the specimen, while the center 
plate rests with one side against the proboscis. 
There are other summit plates following a radial direction, 
which are either attached to the apical pieces or separated from 
them by a belt of small polygonal plates. Their number, 
which varies greatly in different species, depends upon the 
number of primary arms that spring out directly from the 
ody, no matter how often the arms branch afterward. In 
each of them there originate two brachial pieces. As a gen- 
corresponding brachial plates above the arms. Therefore in 
adult specimens, with some little practice, the number of arms 
can be ascertained nearly as well from the dome as from the 
n loo 
bundred apparently irregularly arranged vault pieces, one 
Liscowit that this con- 
