OF WESTEKN SIND. 179 



Genus ILAEIONIA, Dames, 1877. 



Test elongately oval or oviform, subdepressed, more or less convex above, flat or 

 slightly convex below ; margins very thick and tumid. 



Apical disk compact, excentric in front. 



Ambulacra petaloid ; petals short, unequal, lancet-shaped, contracting towards the 

 outer extremity, which is nearly closed. Poriferous zones equal, pores round or slightly 

 oval ; pores of a pair united by a conjugating groove. 



Peristome decagonal, or subpentagonal, with raised rim and special tubercles 

 more or less developed. No floscelle. 



Periproct elongately oval, situated on the upper part of the vertically truncate 

 posterior extremity. 



Ornamentation very uniform ; tubercles small, sunken in deep scrobicules, closely 

 placed, miliary granulation confluent and compact. A more or less well-defined band, 

 devoid of scrobicules, present between the peristome and periproct. 



The distinctive character oi Ilarionia, as pointed out by Dr. W. Dames, consists in 

 the peculiar structure of the peristome. This was described by him * as having a dec- 

 agonal outline which might be represented by an equilateral pentagon from which the 

 angles had been abruptly truncated by short lines ; the long lines, corresponding with 

 the interambulacral areas, being granular, whilst the short lines, which would corre- 

 spond with the ambulacra, are smooth. Furthermore, at the junction of the long and 

 short lines a small smooth tubercle is present, the peristome being consequently sur- 

 rounded by ten of these protuberances. The margin of the aperture is raised and 

 extends far upwards into the body-cavity of the test, the walls corresponding with the 

 interambulacral areas being finely granulated. In other respects the genus unites in a 

 remarkable manner the characters of Echinanthus and Pygorhynchus. 



1. Ilabionia Sindensis, Duncan & Sladen. Plate XXXII, Figs. 9-18. 



Test of small or medium size. Marginal contour elongately oval, well-rounded in 

 front, more contracted behind, and vertically truncate at the posterior extremity. The 

 greatest breadth lies usually midway between the extremities, and is about seventeen 

 twentieths of the length, or in the proportion of 0'85 : 1. The dorsal surface is mode- 

 rately high and flatly convex ; the height being rather more than three fifths of the 

 length, or (in the type specimen) as 0'63 : 1. The position of the apical summit or 

 greatest height of the test is subject to variation, and may either correspond with the 

 apical disk, which is excentric in front, or may be situated between the extremities of 

 the posterior petals, and consequently excentric behind. There is likewise a conform- 

 able variation in the longitudinal profile of the test. In the type the outline is very 

 cylindrical, the median portion of the abactinal surface being almost flat, passing with 

 a well-rounded curve over the anterior extremity, and sloping down posteriorly with a 

 gentle curve tillit meets the abrupt posterior truncation, which is vertical. In tests 



* Die Echiniden der vicentinisclieii und veronesisclieii Tertiarablagerungeii, p. 34. Palseontographica, 

 N. P. V. 1 (xxv.). 



