FROM THE RED CHALK. 101 



Peltastes Wiltshirei, Wright, nov. sp. PI. XL, fig. 1 a — h. 



Diagnosis. — Test subglobose, elevated at the upper surface, flat at the base ; ambulacra 

 narrow, straight, two rows of marginal mammillated granules ; poriferous zones narrow, 

 and slightly flexed ; inter-ambulacra wide, two rows of large tubercles, five in each ; apical 

 disc very broad, margin deeply cut out ; ovarial plates largely incised ; vent elevated ; 

 periprocte prominent, projecting outwards and backwards. 



Dimensions. — Altitude, six tenths of an inch ; latitude, eight tenths of an inch. 



Description. — We owe the discovery of this beautiful Peltastes to the long, careful, and 

 patient study of my excellent friend, the Rev. T. Wiltshire, F.G.S., on the red chalk of 

 England, to whose valuable collection it belongs. The test is subglobose, much elevated 

 on the upper surface, and covered with a very large apical disc ; the base is flat, and the 

 sides are tumid. The ambulacral areas, very narrow and straight, are occupied by 

 two rows of small oblong mammillated marginal granules, about nineteen in each row, 

 separated by a narrow band of fine, close-set granulations, which extends from the base to 

 the summit of the area ; the poriferous zones are narrow and slightly flexed, and the 

 small pores are arranged in oblique pairs, of which there are thirty-eight in each zone. 

 Fig. 1/* exhibits one entire ambulacrum, with its poriferous zones, magnified four diameters. 



The inter-ambulacral areas are wide and largely developed (fig. 1 a, d, e) ; the ovarial 

 and ocular plates of the apical disc cover up much of the upper portion (fig. 1 b, d, e) ; 

 there are ten primary tubercles in each area, of which four are very large, two small, and 

 four smaller ; they are all surrounded by wide areolas (fig. 1 d, e), and around their 

 margins a few large granules are sparsely disposed, about five around the largest plates, 

 three at the central, and two at the zonal side of the plate, as shown in fig. 1 //,. The 

 base is flat (fig. 1 c), about two fifths the diameter of the disc, the mouth-opening is 

 nearly one half the diameter of the test, and the peristome is divided into ten nearly 

 equal lobes by deep incisions ; the numerous small tubercles at the base of the areas, and 

 the larger size of the marginal ambulacral granules, impart to this region of the test a 

 highly ornamented appearance (fig. 1 c). 



The apical disc (fig. 1 b andy) is a large and complicated structure ; the suranal plate lies 

 in front of the vent, and is notched with sections of four elliptical impressions ; the ovarial 

 plates are large and cut in a like manner into similar patterns, the two adjoining plates 

 contributing each one half of the ellipse, so that the sculptured pattern on the entire disc 

 is made up of separate pieces like mosaic ; the oviductal holes are in the middle of the 

 plates and on the right antero-lateral ; the madreporiform tubercle appears like a laceration 

 on the inner side of the oviductal hole — this has unfortunately escaped the eye of our 

 artist, as it looks more like a portion of decayed plate than a veritable natural structure. 

 The ocular plates are likewise large, and have five or six notches round their border, which 

 in like manner join similar notches on the ovarial plates and complete the elliptical pattern 



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