THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[FOURTH SERIES.] 

 No. 42. JUNE 1871. 



XLIX. — On the Base {Pelvis) of the Crinoidca braciiiata. 

 By Prof. Beyrich*. 



Since the investigation of the liy'iwg Pent acri mis by Johannes 

 Miiller, the name of hose has been generally accepted for that 

 part of the or inoidab skeleton on which the radially arranged 

 parts of tlie calyx originate. The base, together with the stem, 

 forms the dorsal surface of the animal ; to the opposite, ven- 

 tral surface belong the calycine apertures, Avhich are double in 

 the living and single in the fossil forms. 



Both in extent and in composition the base of the calyx is 

 subject to multifarious variations. Sometimes it forms a 

 spherically hollowed sac, upon the upper margin of which the 

 basal joints of the radii are inserted ; sometimes it is a short 

 funnel or cone, or a flat cup, which takes only a small part in 

 the Availing of the calycine cavity ; sometimes it seems to have 

 entirely disappeared, either by metamorphoses such as may be 

 demonstrated in the living Comatida', or by amalgamation 

 with the radii, or by an enveloping overgrowth of the latter, 

 as is the case in Eugeniacrinus. Nevertheless the base always 

 remains an essential part of the skeleton, which cannot be 

 imagined as non-existent. A crinoid without a base (which 

 does not exist) would be one in which the radii meet, separate 

 from each other, in the dorsal pole, so that the pole would be 

 surrounded by the first five radial joints. 



The progressive study of the fossil Crinoidea has shown 

 that the form and extension of the base furnishes a non- 

 essential character, in accordance with which we can scarcely 

 form generic divisions ; on the other hand it has become more 

 and more evident that the composition of the base furnishes 

 the most important of all distinctive characters. The arrange- 



* Translated by W. S. Dallas, F.L.S., from tlie ' Monatsbericlit der 

 kon. preuss. Akad. der Wiss. zu IBerlin,' Feb. 1871, pp. .33-65. 



Ann. & Mag. K Hist. Ser. 4. TW. vii. 29 



