100 



Guide to the Invertehrata. 



VIII. 



East Side 



Wall- 

 oase 18. 



Table- 

 case 73. 



Table - 

 case 74. 



Ciiiioidea. which are in the Museum (Table-case 73). It is intended to show 

 GALLEEY the main features in the structure of a simple form of crinoid. 



In Palseozoic seas stalked crinoids abounded : some of the slabs 

 of "Wenlock Limestone in Wall-case 18 show how many different 

 genera and species lived quite close to one another. The British 

 Silurian crinoids are displayed, M'ith labels explaining their 

 structure and classification, in Table - case 73. MastigocrinuSy 

 Thenar ocrimis, Gissocrinus, Periechocrinus, Glyptocrinus, and 

 Taxocrinus are beautiful and characteristic forms. Herpetocrinus, 

 Calceocrinus, Crotalocrinus, and Eucalyptocrinu8 are remarkable for 

 their curious modifications of structure. The British Carboniferous 

 crinoids are in Table-case 74. Here a different type, with a large 

 calyx composed of numerous plates, is seen in Actinocrinus and 

 Amphoracrinus. The crinoids of this period are even more 

 abundant in North America, and some exceptionally fine specimens 

 are shown in Wall-case 18. One may note Gilbertsocrinus with 

 strange drooping appendages, the spiny Borycrinus, and Euclado- 

 crmus with its twisted stem: Some beautiful Devonian crinoids, 

 preserved by pyrites in a dark shale, are shown in Wall-case 17. 

 Above them are specimens of the well-known Lily Encrinite 

 {JEticrtnus fossilis) from the Muschelkalk of Brunswick. 



Conspicuous among Mesozoic crinoids is Extracrinus, of which 

 many magnificent examples from Lyme Regis and elsewhere are 

 exhibited in Wall- case 16. Here we note how colonies were 

 formed of many individuals of only one or two species, as is the 

 case to-day. A portion of such a colony from the Lias of Boll, 

 in Wiirtemberg, forms a beautiful picture in the middle of the 

 case. The stem of this form is said to reach a length of 50 feet; 

 a length of 15 feet is certainly common. The Pear Encrinite 

 {Apiocrimis) from the Bradford Clay of Wiltshire is a strangely- 

 developed type (Table-case 74). In Jurassic and Cretaceous times 

 unstalked crinoids became more common, and remarkable examples 

 are seen in Marsupites, from the English Chalk (Table-case 74), 

 and Uintacrinus, from rather older rocks in North America (slab 

 on the wall). The common unstalked forms, however, are Antedon 

 and Actinometra, which, beginning in the Oolites, occur in vast 

 numbers in modern seas, especially in the Eastern Archipelago. 

 Though unstalked and free-moving when grown up, these crinoids 

 are fixed by a stalk when quite young. 



Crinoids often flourish in such abundance that their remains 



Wall- 

 oase 18 



Wall- 

 case 17 



Wall- 

 case 16 



Table- 

 oase 74 



