90 PEOF. P, M. DTJNCAlSr's EEVISIOIS" OF THE 



M. de Loriol (Ours. Tert. de la Suisse, Pal. Soc. Suisse, 1875, 

 vol. ii. p. 16) considers Micropsis to be synonymous witli tlie 

 Cyphosomatoids with uniserial pairs of pores {Coptosomd); but the 

 beight of so many of the tests of Micropsis, the considerable 

 number of the coronal plates, and the small size of the primary 

 tubercles are distinctive. jS'evertheless it is evident that not 

 only are there species of Goptosoma in Cotteau's list of Micro- 

 psides, for instance M. leridensis, but some require elimination 

 from the family, for instance 3£. Vidali, Cott., which is alto- 

 gether aberrant. 



The ambulacra of the species with four pairs of pores to a 

 compound plate, such as the type species M. Desori, have not the 

 component plates of their symmetrical compound plates arranged 

 as in the genera Cyphosoma and Coptosoma ; on the contrary, the 

 arrangement resembles that of the species of Placodiadema (p. 64), 

 which have numerous components to an ambulacral plate. The 

 compound plate is high, and is composed of a small, low, broad 

 adoral primary, very low at the median suture of the compound 

 plate ; or it may be a demi-plate ; next comes a large primary, 

 comprising most of the tubercles and the angle of the median 

 suture ; then succeed aborally, two low broad primaries, their 

 adoral sutures being rather curved, convexity adorally. (See 

 Quart. Journ. Geol. Soc, vol. xli. p. 431, fig. 8.) This arrange- 

 ment may also occur when there are five pairs of pores to a com- 

 pound plate ; and then the last pair of pores is in a low broad 

 primary, which resembles the aboral primaries of the other 

 plate. This kind of arrangement is not seen in any species of 

 CypJiosoma ; and therefore there is a good physiological diff'erence 

 between the species with numerous pairs of pores and those 

 with few which have been included in Micropsis and Cyphosoma 

 or Coptosoma. 



The species with three pairs of pores in an ambulacral plate 

 may be grouped around Micropsis venustula, Dune. & Sladen, 

 1884, Pal. Ind. ser. xiv., Foss. Ech. Sind, p. 119, pi. xxii. figs. 1-7. 

 The apical system has large basal plates ; a radial enters the ring, 

 and the periproct is large and deformed ; the amulacra are narrow, 

 and bave two vertical rows of small perforate and crenulate pri- 

 mary tubercles and two vertical rows of secondary tubercles ; 

 the plates are high and compound ; the adoral plate is a large 

 primary carrying the bulk of a tubercle, and the other plates, 

 placed aborally to it, are low broad primaries. The difierence 



