FROM THE INFERIOR OOLITE. 153 



to the upper surface ; mouth opening small, situated in a depression ; peristome decagonal 

 and unequally lobed. 



Dimensions. — Height, two fifths of an inch ; transverse diameter, nine tenths of an 

 inch. 



Description. — This beautiful Hemipedina is a very rare form, having only found 

 one specimen of the species during the many years I have collected from the locality where 

 it was discovered. 



The tubercles of the ambulacra are nearly as large as those of the inter-ambulacra, which 

 imparts a very regular appearance to the test (fig. 3 b, c). 



The ambulacral areas are narrow, about one third the width of the inter-ambulacral ; 

 on the margins are two rows of tubercles, about twenty in each row; they are very 

 uniform in size, and arranged in a straight line throughout the area (fig. 3 b, c, d) ; the 

 bosses abut against the poriferous zones, but they are separated from each other by a deli- 

 cate, double line of granules, which extends on each side of the central suture (fig. 3 d), 

 every third granule between the tubercles being larger. The poriferous zones are narrow, 

 and slightly undulated, in consequence of the ambulacral tubercles being placed so close 

 to the avenues, without the intervention of any granular space between to prevent the 

 encroachment of the tubercles on them (fig. 3 b, c, d). 



The inter- ambulacral areas are four times as wide as the ambulacral ; at the equator, 

 each of the large plates of these areas has one central primary tubercle, and at its centro- 

 sutural side, one secondary tubercle, and between the central tubercle and the zones two 

 rows of granules (fig. 3 d) ; from the peristome to the equator there are therefore four 

 rows of tubercles (fig. 4 d, c), but as the secondary tubercles diminish in size above the 

 equator, and disappear on the upper surface, there are only two rows of tubercles near the 

 circumference of the apical disc (fig. 3 b) ; the bosses are not very prominent ; the tubercles 

 small, the minute granules forming circles around the rudimentary areolas (fig. 3c/); 

 there are fourteen primary tubercles and ten secondary tubercles in each row, and from 

 four to five pairs of pores in each of the large inter-ambulacral plates. 



The base is very concave, and the small mouth opening lies in rather a deep depression ; 

 unfortunately it is filled with a hard mass of pisolite, which cannot be dislodged without 

 risk to the shell (fig. 3 c). 



The discal opening is small, but all the plates of the disc are absent. 



Affinities and differences.- -The regularity of the ambulacral tubercles, and the nearly 

 uniform size they have in both areas, distinguishes this species from its congeners ; the 

 fact that the inter-ambulacra have four tubercles abreast at the equator, forms a good 

 diagonistic character, and serves to distinguish it from other allied species found with it in 



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