OF WESTERN SIND. 137 



Illustrations of the Species in Plate XXV. 



Fig. 33. Abactinal view of the test : natural size. 



34. Abactinal view of the test : magnified four times. 



35. Actinal view: magnified four times. 



36. Longitudinal profile : magnified four times. 



37. Apical disk: magnified. 



Gemis SISMONDIA, Desor, 1857. 

 Test of small or medium size, subpentagonal or ovoid, depressed, inflated at the margin. 

 Ambulacral summit central or subcentral; apical system compact, four generative 

 pores. 



Ambulacra petaloid, usually long, and more or less open at their extremity. Pores 

 united by a conjugating furrow. Interambulacral areas of the test supported internally 

 by a pair of strong, complex, vertical partitions. 

 Peristome central, sometimes impressed. 



Periproct rounded, placed between the peristome and the margin. 

 Prior to the establishment of this genus by Desor, the species included therein 

 had usually been placed in the genus Echinocyamus. Sismondia is distinguished by 

 the form of the test, by the well-developed petaloid ambulacra, by the conjugate pores, 

 and by the greater development of the internal partitions. 



1. Sismondia poltmorpha, Duncan & Sladen. Plate XXV, Figs. 1-13. 



Form depressed, marginal contour subovoid, with a tendency towards the penta- 

 gonal, the outline being slightly contracted anteriorly and feebly truncate posteriorly. 

 Abactinal area almost plane, excepting the costulate interporiferous areas of the petals. 

 The height of the test is small and is rather less posteriorly than anteriorly, the abac- 

 tinal surface sloping slightly from the apical centre of the disk to the posterior extremity. 

 The margin is thick and well rounded, almost tumid. The actinal surface is slightly 

 concave, the test being regularly and evenly depressed around the peristome. 



The apical system is subcentral or very slightly excentric in front. The apical 

 disk is flush with the test and comparatively broad. There are four large genital 

 plates all touching one another; the genital pores are large and round, and the 

 anterior pores are much nearer together than the posterior. There is no true 

 madreporiform body, but a single, round, madreporic pore is present, situated rather 

 nearer to the right anterior generative pore than the centre of the apical system. 

 The ocular plates are very small and somewhat escutcheon-shaped, with the apex 

 directed away from the disk ; and they occupy a place at the junction of two neigh- 

 bouring genital plates. The ocular pits are minute and elongate or slit-like ; and in 

 well-grown specimens the portion of the plate on the outer side of the pit away from the 

 centre is somewhat elevated, and forms a slightly raised embankment round the aperture. 



The ambulacral petals are broad, subequal, equal in length to two thirds of the 

 distance between the apex and the margin ; widely open at the extremity, where the 

 poriferous zones are slightly bent outward. The poriferous zones are equal ; the pores 



