ECHINODERMATA 31 



when detached, are the " St. Cuthbert's beads" of story (tig. 

 6, 5).* In Platycrinus the stem is compressed, and the arti- 

 cular surfaces are elliptical. In the genus Pcntacrinus, which 

 commences in the lias, the sculpturing of the articulations is 

 more complex (fig. 6, 8), but it is quite simple in the other 

 modern genera. The body of the Crinoid is composed of poly- 

 gonal plates forming a cup, which is covered by a canopy of 

 smaller plates. The mouth is often proboscidiform ; the anal 

 orifice is near it. The five arms which crown the cup are 

 sometimes nearly simple, but feathered with slender, jointed 

 fingers ; in other genera they divide again and again, dichoto- 

 mously ; and in two remarkable Silurian forms, A nthocrinus 

 and Crotalocrinus (fig. 6, 4), these subdivisions are extremely 

 numerous, and the successive ossicles are articulated to each 

 other laterally, forming web-like expansions, similar in appear- 

 ance to the coral Fenestrella (fig. 3, n). Other remarkable 

 Silurian Crinoids belong to the genera Glyptocrinus, EucalyiJ- 

 tocrimis, Geocrinus (the " Dudley Encrinite") and Caryocrinus. 

 Several are common to the Silurian and Devonian, as Me- 

 locrinus, Cyathocrinus, and Rhodocrinus ; the two last, and 

 PoUriocrinus, extend into the carboniferous formations. Cu- 

 pressocrinus and some others are peculiarly Devonian ; Platy- 

 crinus, common to Devonian and coal formations ; and many 

 genera (including the " nave Encrinite" — Actinocrinus, Gil- 

 bertsocrinus, and Woodocrimts), are proper to the carboniferous 

 limestone. The famous " lily Encrinite" (Encrinus entrocha, 

 fig. 6, 6) is characteristic of the middle trias, or " muschel- 

 kalk ;" the " clove Encrinite" {Eugeniaerinus, fig. 7, 9) abounds 

 in the Oxfordian oolites of Germany ; Apiocnn us, Milleri- 

 crinus, and several forms related to Comatula — e.g., Pterocoma 

 and Saccosoma — are also peculiarly oolitic. The " tortoise 



* Casts, in chert, of the canal which passes down the crinoidal column are 

 called " screw stones;" and those limestones which abound in columns and 

 detached joints are called " entrocha! marbles." 



