292 CYSTOIDEA, BLASTOIDEA, AND HOLOTHUKOIDEA. 



plates of the test are all solid and imperforate. In the 

 genus just mentioned the calyx is globular, composed of 

 comparatively few plates, which have a tolerably definite 

 arrangement, there being three basals, succeeded by two 

 ranges of pentagonal plates. There is a " valvular pyramid " 

 of five small plates, but the arms are unknown. The genus 

 Malocystites, from a very low horizon in the Silurian series 

 (Chazy Limestone), has also an imperforate test, and differs 

 from Cryptocrinus chiefly in having the calyx composed of 

 an indefinite series of plates. Another form of the same 

 group is the Trocliocystilcs of Barrande, from the "Primordial" 



Fig. 174. A, Echinosphcerites aurantium. B, Cryptocrinus Icevis. c, Ecldnoencrinus SenJcen- 

 bergi. D, Echinoencrinus armatus. E, One of the "pectinated rhombs " of the last, enlarged. 

 F, Holocystites cylindricus. v, Valvular pyramid Silurian. All the specimens are viewed 

 from one side. (A, B, and c are after Von Buch ; D is after Edward Forbes ; and F is after 

 Hall.) 



(Upper Cambrian) of Bohemia. This last-named type is 

 of special interest from its high antiquity, the only other 

 Cystoids of like age being the Eocystites of the " Acadian 

 group "of St John's and the Protocystites of the " Menevian 

 group" of St David's, both of which are only known by 

 detached fragments, and are ill understood. The aberrant 

 genus Lichenocrinus, of the Lower Silurian, may also possibly 

 belong to this group of the Cystideans, but if so, it forms the 

 type of a quite peculiar section. We may temporarily place 



