Dr. T. Wright on the Cidarida? of the Oolites. 271 



are not deep. None of the specimens that we have seen possess 

 the apical disc, but the vacant space left by the absence of the 

 ovarial and ocular plates proves that this part of the test was well 

 developed. 



Affinities and differences. — In its pentagonal form it is allied 

 to D. depression, but its secondary tubercles and double file of 

 pores form a good diagnosis between D. subangulare and other 

 species of the same genus. 



Locality and stratigraphical range. — We know this species only 

 from the Coral Rag of Wilts and Oxford ; in Germany it is found 

 in the same stages at Thurnau and Muggendorf ; and in Switzer- 

 land it is obtained from the " Terrain h chailles " of the valley of 

 the Birse, of Blochmont and of Weissenstein. 



History. — First figured by Goldfuss, afterwards more accu- 

 rately described and figured in detail by M. Agassiz, and now 

 described as a British species for the first time ; the specimens 

 previously catalogued under this name having been D. depressum 

 and not D. subangulare. 



Diadema pseudo -diadema, Agass. PL XII. fig. 1 a, b, c. 



Syn. Cidarites pseudo-diadema, Lamarck, Syst. Anim. sans Vert. 



torn. hi. p. 385. 

 Diadema Lamarckii, Desmoulins, Tabl. Synopt. p. 316. No. 18. 

 Diadema pseudo-diadema, Agassiz, Echin. Foss. t. 17. fig. 49-53. 



Test hemispherical, depressed; interambulacral arese with pri- 

 mary and secondary tubercles ; ambulacral arese with primary 

 tubercles and a few scattered rudimentary ones. Mouth 

 large and decagonal; margin deeply notched; apical disc 

 large ; spines long and needle-shaped. 



Height 1 inch and /^ths, transverse diameter 2 inches and 



Description. — This fine species has a hemispherical form, much 

 depressed at the anal pole and flattened at the base. The ambu- 

 lacral arese are straight and well developed, and furnished with two 

 rows of primary tubercles from 18-20 in each row; between 

 these a zigzag line of small secondary tubercles extends two- 

 thirds up the arese ; the poriferous avenues are not well defined ; 

 the pores are disposed in pairs ; between each pair of holes there 

 are elevated smooth tubercles forming a range of small bead- 

 like bodies which define the limits of the arese; at the base 

 the pores fall into double and triple files. 



The interambulacral arese are more than twice the width of 

 the ambulacral, and are furnished with two rows of large pri- 

 mary crenulated and perforated tubercles, and several rows of 

 secondary tubercles likewise crenulated and perforated ; down the 



