IN THE MORPHOLOGY OF THE CTSTIDEA. 13 



altogether absent, as in Hylocystis, and altbougli apparently 

 interradial in position in some types, they seem in others to be 

 definitely related to the ambulacra. They would probably be 

 best considered as perisomic plates, without any distinct orienta- 

 tion ; and in some forhis they are succeeded by others of the 

 same character. Such, for example, are the small plates round 

 the peristome of Gryptocrinus and Apiocystis elegans, and the 

 larger ones of Glyptocystis pennigera ; while in many Cystideans 

 the whole body is made up of these irregularly arranged perisomic 

 plates, just as in the Psolidae among the Holothurians, and all 

 tz'aces of a calyx comparable to that of a Crinoid have dis- 

 appeared. 



Under the name of Caryocystis pumila, Eichwald * has figured 

 a curious form with the body covered by four, or perhaps five, 

 alternating series of plates. The anus is low down, notching two 

 of the plates of the second series, which I take to be the basals, 

 just as in Semicosmites, Echinoeiicrinus, and their allies (PL I. 

 figs. 1-6). In the rare genus Pr«mocys^2s t from Dudley there 

 are at least three regular alternating series of plates, which 

 correspond respectively to the infrabasals, basals, and radials of 

 Ecliinoencrinus. The same is the case in Macrocystella %, Cal- 

 laway, of Tremadoc age, and also in another member of the 

 Primordial fauna, i^c7^e;^o^V/e5, Barrande §. Two others of Bar- 

 rande's genera, Mimocystis and JELomocystis, present similar 

 characters ||, and would seem, indeed, to belong to the same group 

 as JEchinoe7icrinus, as already suggested b}^ Barraude, but they 

 are not sufiiciently well preserved for this to be made out with 

 certainty. 



Enough has been said, however, to show that there are a con- 

 siderable number of Cystids which are characterized by the 

 possession of a dicyclic calyx like that of a Crinoid, and that 

 these may be grouped round two central forms, Garyocrinus, 

 with hexamerous symmetry, and Echinoencrinus, which is penta- 



* ' Lethtea Eossica,' 1860, vol. i. sect. 1, p. 629, pi. xxxii. fig. 19 b. 



t Mem. Greol. Survey, vol. ii. pt. 2, pi. xvi. 



X " On a new Area of Upper Cambrian Eocks in South Shropshire, with a 

 Description of a new Fauna," Quart. Journ. Geol. Soc. 1877, vol. xxxiii. p. 669, 

 pi. xxiv. fig. 13. 



§ ' Systeme Silurien du Centre de la Boheme,' vol. vii. 1887, Cystidees, p. 183 

 pl.i. 



II Ibid. pp. 77, 160, 164, pi. xxviii. 



