Some new Upper Greensand Echinoderms. 21 



and below, the interspace is closely and irregularly granulated. 



Shell round the mouth inflected. Apical opening pentangular ; 



width 6 lines. 

 Lat. ]^ inch, alt. f inch. 



Most nearly related to D. Malbosii (Desor),but differs in the 

 small size of the mouth, in having the rows of tertiary tubercles, 

 in the greater number (especially of ambulacral) tubercles, &c. 



Diadema (subg. Pseudodiadema) inversum. 



Circular, depressed, flattened above, concave below. Apical 

 opening pentangular. The greatest inflation is above the 

 middle of the shell. Mouth very deeply sunk. Ambu- 

 lacral tubercles arranged in two rows of about seventeen 

 each, nearly as large as the interambulacrals, except on the 

 upper surface, where they become much smaller, and are 

 scarcely elevated : the rows are separated on the lower part 

 of the shell by a single zigzag row of granules, — round the 

 circumference by two rows; the space above naked. The 

 areolae are large circles, which are confluent; they are in- 

 distinctly radiated. On the outer side of the bosses, on the 

 lower half of the shell, descend three wide deep grooves, 

 each to a pair of pores, the inner one of which they almost 

 obscure, thus giving the tubercles a remarkable semiradiated 

 appearance. The zones are straight, and the pores in single 

 file throughout. Except on the upper part, each pair of pores 

 appears to be surrounded by a little ring, which is divided by 

 the septum being also elevated. Interambulacral tubercles 

 in two primary rows of about sixteen each ; they are each 

 flanked externally by a secondary row of about nine ; outside 

 of these, on each side, is a tertiary row of two or three times 

 the number. The tubercles are radiated, and on the upper 

 part of the shell surrounded by a row of granules ; from the 

 areolae enlarging, these become, at the circumference, a double 

 row of granules. The upper parts of the intermediate spaces 

 are naked and rather hollow. 



Lat. 1£ inch, alt. T 9 g inch; apical apert. ^ inch; oral apert. 



A inch - 



Most nearly related to D. Barretti (Woodw.). It differs, 

 however, in having the tertiary tubercles, two or three of which 

 are placed on each plate, in the greater number of tubercles, 

 the different inflation, small mouth, and in having but half as 

 many rows of granules. 



Rare. Coll. University. 



From the oral opening being mostly filled with phosphate of 

 lime, not more than fifteen tubercles in a row will commonly be 

 visible. 



