1 1 PSEUDODI ADEMA. 



The following Table exhibits these Sections, and shows at the same time the arrangement of 

 the tubercles in the unigeminal and bigeminal groups. 



Section a. — Fores unigeminal in the upper part of the zones: 



Examples. 



a. Two rows of primary tubercles only") -r, , ,. 7 7 



, . , , - \ rseudodiadema depressum. 



m the mter-ambulacrai areas ) 



b. Two or four rows of primary tuber- \ 



SPseudodiadema hemisphcericum. 



cles, and two or four rows of( 



/■J 



smaller secondary tubercles in the r 

 inter-ambulacral areas ) 



Section b. — Pores bigeminal in the upper part of the zones: 



a. Two rows of primary tubercles, and\ 



two rows of small secondary ( 



,11 • ,1 • , 11 1 } Pseudodiadema versipora. 



tubercles, m the mter-ambulacral 1 -^ 



areas / 



b. Four rows of primary tubercles in ") „ ^ -,. -, - , 



^, . ^ 111 c Pseudodiadema vanolare. 



the mter-ambulacral areas ) 



A. Species from the lAas. 



Pseudodiadema Mooreii, Wright. PL VI, fig. 1 a, b, c, d. 



DiADEMA Mooreii. Wright, Annals and Magazine of Natural History, 1854, 2d series, 



vol. xiii, p. 171, pi. 12, fig. 3. 

 — — Morris, British Fossils 2d edit., 1854. Note on additional species 



. of Echinodermata. 



DiADEMOPSis Mooreii. Desor, Synopsis des Echinides Fossiles, p. 81. 



Test circular, depressed ; ambulacral tubercles smaller than those of the inter-ambu- 

 lacral areas ; plates of the test covered with a small, wide- set, prominent granulation ; 

 mouth large and decagonal j anal opening large ; apical disc of moderate size. 



Dimensions. — Height, one fourth of an inch ; transverse diameter, six tenths of an 

 inch. 



Description. — There is much difficulty in distinguishing some of the smaller Diademas 

 from each other, inasmuch as the young condition of many of the larger species so closely 

 resembles the adult state of others, that it is only after obtaining a number of individuals 

 of different species in the various phases of their growth, that the naturalist feels himself 



