] 20 PSEUDODIADEMA. 



E. Species from the Cornhrash. 

 PsEUDODiADEMA Bailti, Wright, nov. sp. PI. VII, fig. 1 a, b, c, d, e, f, g. 



Test sub-pentagonal, depressed ; ambulacral areas narrow, a little more than half the 

 width of the inter-ambulacral, with two rows of primary tubercles, smaller than those of the 

 inter- ambulacra ; inter-ambulacral areas with two rows of primary tubercles, which 

 suddenly diminish in size above the equator ; poriferous zones narrow, and unigeminal 

 throughout ; mouth opening large, peristome nearly equally decagonal. 



Dimensions. — Height, three tenths of an inch; transverse diameter, seven tenths of an 

 inch. 



Description. — This beautiful little Diadem, like the preceding species, presents such a 

 uniformity of structure, and such a total absence of prominent characters, that it is 

 extremely difficult to form an accurate diagnosis of its specific form. 



The test is small, depressed, and sub-pentagonal (fig. \ a,h); the ambulacral areas are 

 prominent, and rather more than half the width of the inter-ambulacral ; they support two 

 rows of primary tubercles, rather smaller than the inter-ambulacral tubercles, of which 

 there are eight in each row ; a central, zigzag line of granules separates the two rows of 

 tubercles from each other (fig. 1 /), and short, transverse, granular branches separate the 

 areolas of the larger equatorial tubercles ; on the upper part of the areas the tubercles 

 become very small; the poriferous zones are straight and narrow (fig. 1 e), and the pores 

 are strictly unigeminal throughout (fig. 1 /) ; there are five pairs of pores opposite one of 

 the larger inter-ambulacral plates, and from three to four pairs opposite the ambulacral 

 plates (fig. 1/). 



The inter-ambulacral areas are nearly twice the width of the ambulacral ; they are 

 occupied by two rows of primary tubercles, there being eight tubercles in each row ; from 

 the peristome to the equator the tubercles gradually increase in size (fig. \ d), but above 

 the equator they diminish rather suddenly in magnitude (fig. 1 e), so that the tubercles on 

 the upper parts of the areas are small in proportion to those at the equator and base of 

 the test (fig. \d)\ the areolas are wide; the bosses are large, conical, and prominent 

 (fig. 1 d, f, g) ; they are confluent above and below, but laterally they are bounded by 

 semicircles of granules (fig. 1 g), five or six granules, with a few other microscopic ones, 

 forming incomplete scrobicular semicircles around their sides ; the miliary zone is narrow, 

 and formed only by the granules just described; on the upper part of the area the 

 granules almost entirely disappear, and the surface of the plates is naked near the point 

 where they approach the disc (fig. 1 e) ; the summit of the conical bosses is crenulated 

 (fig. 1^^), and the tubercle is small and perforated (fig. 1/). There are no secondary 

 tubercles at the base of this species. 



