I. Dinocystis Barroisi. 



V. 547 



Systematic Position. 



Discussion of the meaning of the above-mentioned structures, and 

 of the affinities of the genus, must be postponed until Edrioaster has 

 been decently described and figured. I may, however, anticipate by 

 saying that the Condroz form is clearly a close ally of Edrioaster, 

 but that it may be distinguished from that genus, as now known, by 

 the tenuity and flexibility of the peripheral area of the abactinal 

 surface, which area in Edrioaster is formed of plates no less solid 

 than those in the interradial areas of the actinal surface. 



Edrioaster and Dinocystis may be separated from the Agelacrinidse 

 and Cyathocystidse, as a family Edrioasteridse, by the absence of 

 a definite border defining the actinal surface, and by the passage of 

 the radial grooves on to the abactinal surface. We may therefore 

 give the following diagnosis of 



Dinocy stis, 1 gen. nov. 

 An Edrioasterid with the peripheral region of the abactinal surface 

 composed of a thin flexible integument containing narrow im- 

 bricating ossicles. 



Genotype : D. Barroisi, 2 sp. nov. ( = Agelacrinus, sp., Mourlon), 

 Upper Devonian, Psammites du Condroz, Belgium. 



The characters of the species are of course those of the above 

 description, but one may allude specially to the relatively narrow 

 radial grooves, and to their consistent sinistral curvature. The 

 holotype is in the British Museum, registered E 7,582. 



EXPLANATION OF PLATE XXI. 

 Dinocystis Barroisi. 

 [All the drawings are from specimens in the British Museum. Figures la, lb, 2a, 

 2c, 3, 4, 5, 6a, 6b are based on photographs by Mr. J. Green ; the other figures 

 are by Mr. G-. C. Chubb. All figures are natural size, except lc, 2d, 2e, 2f, 

 which are x 4 diam., 7b, which is x f, and 7c and 7d, which are x 2 diam. 

 In all the complete views the right and left of the specimen correspond with the 

 right and left of the observer.] 

 Fig. 1 (E 7,581). a. Actinal surface ; anus distinct in lower interradius. 



b. Abactinal surface ; radial grooves are seen at top and on left ; imbricating 



plates of peripheral area well shown. 



c. Distal portion of a radial groove drawn from the specimen. 



Fig. 2 (E 7,582). a. Actinal surface ; impressions of interradial plates are clear. 



b. Seen from anterior end ; the groove in the middle is anterior. 



c. Abactinal surface ; the trace of the frame is seen between east and south of 



the drawing ; the coarse radial folding of the peripheral area and the 

 fine folding of the central area are seen between S. and S.S.W. ; portions 

 of radial grooves are visible at both top and bottom. 



d. Portion of anterior radial groove, drawn from specimen just where the 



groove first curves sharply to the left in Fig. 2a ; shows knobs and 

 transverse ridges. 



1 AeivSs, terrible, wondrous. It might astonish anyone not acquainted with the 

 true structure of Edrioaster. 



2 In honour of Dr. Charles Barrois, whose valuable work on Devonian rocks and 

 fossils, of other districts, must be held to excuse this dedication to him of a fossil 

 with which be has had no obvious connection. The undesirability of applying the 

 names of persons to species, without cogent reason, has been maintained by me so 

 consistently that it will be understood that these names, suggested by Dr. Jaekel> 

 are here adopted merely so as to avoid any possible confusion. 



