222 REPORT OF NATIONAL MUSEUM, 1901. 



III.— DIVISION OF STRATIGRAM 1 10 PALEONTOLOGY. 

 A. Section of Invertebrate Fossils. 



The exhibit of the section of invertebrate fossils formed two series 

 comprising the more interesting crinoids and cephalopoda, the first 

 being illustrated by 94 and the second by 156 genera. The object 

 of the collections was to illustrate by specimens and descriptive labels 

 the anatom} r and generic characters of the hard parts of these animals 

 as known to paleontologists, and incidentally to illustrate the methods 

 of installation practiced in this section. 



Each series began with an introductory label defining the essential 

 characters of each class of organisms. As many technical words were 

 involved in the description, a second series of labels was prepared, in 

 which the terms were defined and which were accompanied by speci- 

 mens on which the parts referred to were artificially colored. As it 

 may be desirable to build up similar series for other exhibits, some- 

 time in the future, the transcript of the introductory and explanatory 

 labels is given below. Plates 62-69 show the character of the mate- 

 rial comprised in the crinoid series. 



This exhibit was comprised in the five screen cases indistinctly 

 shown at the left in Plate 58. 



INTRODUCTORY LABEL. 

 CLASS CRTNOIDEA. 



Crinoids, or sea lilies or stone lilies, are marine animals related to the starfishes, 

 and like them have in the outer integument a skeleton of calcareous ossicles. A 

 normal crinoid consists of a crown attached by its dorsal or aboral extremity to a 

 xtf/m, which is fixed to the sea floor or to some solid body by a root. They are gre- 

 garious, locally restricted, animals, have existed since Cambrian time, and live in 

 the seas, ranging from shallow water down to about 3 miles beneath the ocean 

 surface. In Paleozoic time they had greatest development, and their separated 

 ossicles occasionally form beds of limestone of considerable thickness. In the Car- 

 boniferous rocks of the Mississippi Valley crinoids are often well preserved and good 

 crowns are not rare. More than ?>00 species are known from the vicinity of Burling- 

 ton, Iowa. 



The crinoids, from a phylogenetic standpoint, are divided into the subclasses 

 Monocyclica and Dicyclica, and these divisions are again separated into six orders, 

 live suborders, and two grades, all of which are here illustrated by specimens. Of 

 recognized genera there are upward of 240. 



SPECIAL EXPLANATORY . LABELS. 

 THE CROWN. 



(See Plate 62.) 



The crown consists of the dorsal cup or shortly cup (colored blue), the legmen, 

 sometimes called disk or vault (red), and the bracliia or arms (yellow), which are 

 generally provided with pinnules (Mack ), and often there is an anal tube (brown). 

 24185. Platycrinus hemisphericus. Lower Carbonic. 

 24191. Cyathocrinus multibrachiatus. Lower Carbonic. 



24163. Batocrinus wachsmuthi. Lower Carbonic. The brachia are removed 

 to show the tegmen and anal tube. 



