REPORT ON THE CRINOIDEA. li?, 



sively througli the Jurassic period, aad died out in the Lower Neocomian. Their phice 

 was taken by the Bourgueticrinidse, which were formerly associated with them into one 

 family. We have no certain evidence of the occurrence of the typical genus Bourgueti- 

 crmus in other than Cretaceous rocks ; though stem-joints which have been referred to 

 this genus occur both in Jurassic and in Eocene deposits. It is not unlikely, however, 

 that they belong to Thiolliericrinus or to Rliizocrinus respectively. The latter genus, 

 which is represented by two living species, is probably exclusively confined to the 

 Tertiary rocks, except perhaps for the so-called Boiirgueticrinus alabamensis from the 

 Cretaceous formation of Alabama, U.S.; and some of the stem-joints hitherto referred to 

 Rhizocrinus or to Bourgueticrinus may possibly belong to Bathyoinus, no calyx of 

 which has yet been found in the fossil state. 



As regards the fossil Holopodid^, there are Micropocrinus of the Italian Miocene, 

 Cyathidium in the Chalk of Faxoe, the singular Gymnocrinus in the Oxfordien of 

 France and Switzerland, and lastly in the Middle Lias Cofylecrinus and Eudesicrinus ; 

 while Edriocrinus from the Upper Silurian and Devonian, a tyjje much resembling 

 Holopus in character, is a proof of the great antiquity of these sessile Crinoids. 



The Pentacrinidse are remarkable for their long geological history. The type genus 

 Pentacrinus first appears in the Trias, together with the short-lived Encrmus. It per- 

 sisted through the whole of the Secondary and Tertiary periods, and is represented by 

 eight species at the present time. On the other hand, Extracrinus with its characteristic 

 stem, dic}clic base, and peculiar arm-divisions is confined to the Lias and Lower Oolites, 

 unless, as I am disposed to think, the Pentacrinus asteriscus which has been found in the 

 Western Territories of the United States associated with Alpine Trias fossils and Spirifera, 

 is also to be refexTcd to this genus. Balanocrinus, kuown as yet only by stem-joints, 

 ranges from the Middle Lias to the Lower Neocomian. The remaining genus Metacrinua 

 is confined to Oceania and the shallower parts of the Pacific, and is at present unknown 

 in the fossil state. 



The general character of the fossil Pentacrinidse is essentially the same as that of 

 their recent representatives, except that they often had much longer stems which 

 sometimes reached as much as 50 or even 70 feet ; while the number of arms was 

 frequently limited to ten, which is not the case in any recent species but Pentacrinus 

 naresianus {Pis. XXVIII. -XXXa.). Some of them also appear to have been devoid of 

 external basals. But in two cases, at any rate, Pentacrinus dixoni and Pentacrinus 

 fishen, this is due to en-or ; for the basals have been overlooked and therefore described 

 as absent.^ 



Three genera of the Comatulidse, Antedon, Actinometra, and Eudiocrinus are known 

 in the fossil state. The last named is at present limited to the Lower Neocomian of 



1 Oil the supposed Absence of Basals iu the Eugeniacrinidae and in certain tther Neocriuoids, Ann. and Mag. Nut. 

 Hist, 1883, ser. 5, voL xi. pp. 327-334. 



