102 A Guide to the Zoological Collections in the 



spond with any hitherto described species or genera, with 

 the exception of an Astroschema {Astroschema Jlosculus) 

 from 88 fathoms in the Bay of Bengal, 



3. ECHINODERMATA CRINOIDEA (SEA-LILIES, FEATHER- 

 STARS). 



[eastern m^XU^QZ 27]. 



The Crinoidea somewhat resemble the Ophiuroidea, 

 especially the Astrophytidse, in external form, consisting 

 of a central disk, in which the viscera are lodged, and of 

 slender arms radiating from the disk, which lodge the 

 ambulacral canals : but the disk of the Crinoids, instead 

 of being flat and depressed, is either conical or cup- 

 shaped, and is often attached by a long stalk ; and the 

 arms are divided from their base into numerous feather- 

 like branches. 



There are two families of Crinoidea— the Pentacri- 

 nidse or stalked Crinoids, and the Comatulidae or free- 

 swimming Crinoids, which are stalked only in the young 

 state. 



ist. The principal external characters of the Pentacrl- 

 nidSB may be learned from an examination of the speci- 

 men of Metacrinus in Case 27. In Metacrinus we find a 

 long stalk by which the animal is fixed, back downwards : 

 it consists of a series of pentagonal stony (calcareous) 

 segments joined together one above another : at regular 

 intervals along the stalk are seen whorls of similarly 

 segmented branchlets known as "cirri". At the end of 

 the stalk comes the disk, which consists of a small stony 

 (calcareous) cup placed mouth upwards. From the edge 

 of the disk spring five arms, which are built up of stony 

 segments, and each of which divides and subdivides 

 several times into long branches fringed on both sides 

 with feathery processes known as " pinnules ". The 

 concave inner surface of the cupped disk is covered 

 by a thick leathery skin, and in the centre of it can be 



