FROM THE UPPER GREENSAND. 175 



sides rounded ; ambulacra narrow, flexed, two rows of marginal, closely set, mammillated 

 granules, with intermediate granulation ; poriferous zones flexed ; pores small, oblique, 

 unigeminal ; inter-ambulacra wide, tubercles large and prominent above, four or five in a 

 row. Apical disc thick, gibbous, subcorneal ; sutural impressions deep, punctuations large, 

 vent circular, periprocte elevated. 



Dimensions. — Specimen a. Altitude, two lines ; latitude, four lines. 

 „ b. Altitude, five lines ; latitude, six lines. 



Description. — The type specimens of this species figured by Professor Agassiz and 

 M. Cotteau, from the Cenomanian of France, have a more elevated gibbous test 

 than any of the specimens referred to Salenia gibba that I have seen from the Upper 

 Greensand of England. The shell is small and circular, the upper surface elevated, 

 the under surface flat, and the sides inflated. The ambulacral areas are narrow, and 

 flexed in their upper third ; they have two rows of mammillated marginal granules set close 

 together, from eighteen to twenty in a series (fig. 4 e), and the surface of the space 

 between the granules is covered with a microscopic granulation. The poriferous zones 

 are depressed, and follow the flexures of the areas ; the pores are small, round, and 

 unigeminal, and disposed in oblique pairs, the two pores forming a pair being separated 

 by a septal granule (fig. 4 e). 



The inter-ambulacral areas are wide, and the tubercles, of which there are four or 

 five in a series, are large, prominent, and distant at the upper surface, and small, 

 granuliform, and closely set together below (fig. 4 b and e); the miliary zone is narrow and 

 sinuous, and provided with unequal granules ; some of these are large and mammillated, 

 and disposed around the primary tubercles in incomplete circles; others are smaller, and 

 fill the lower portion of the zone with a sparse granulation. 



The apical disc is thick, irregularly round and prominent (fig. 4 c, d), and the plates are 

 unequal. The sutures are open and incised, and the punctures deep ; in some specimens 

 figured by M. Cotteau the disc is thick, gibbous, and subcorneal, and the impressions are 

 wide and deep ; the surface of the ovarial plates has small attenuated elevations, which 

 converge at the centre of the plates. The ocular plates are sub-triangular, and appear to 

 be perforated in the middle ; the sur-anal plate is large and thick, and the oviductal lobes 

 pierce the centre of the plates (fig. 4>d). The vent is sub-circular, and the periprocte 

 prominent, with an annular projecting border. 



The mouth-opening is small, rather more than one third the diameter of the test 

 (fig. 4 b). The peristome is slightly incised, and the oral lobes are nearly equal. 



Affinities and Differences. — In his ' Synopsis des Echinides fossiles/ my friend 

 Professor Desor considers 8. gibba as simply a variety of 8. scutigera ; it appears, however, 

 to have a more inflated gibbous form, with more flexuous ambulacra, a thicker apical 

 disc, more unequal in outline, and marked with larger and deeper perforations ; and the 

 mouth-opening is likewise proportionally smaller. 



The structure of the apical disc allies S. gibba to S. Bourgeoisi ; the test of the 



