244 ■ CATOPYGUS 



and granules on the ambulacral and inter-ambulacral areas magnified six times ; and 

 fig. 2 exhibits the more developed form the tubercles assume on the basal plates, and the 

 manner they are encircled by rows of granules. It is only on very fine specimens, such 

 as some I have obtained from the Chloritic Marl of Chard, that I have been able to see the 

 surface anatomy of the plates, such as I have figured and described it; the Upper- Greensand 

 fossils are spoiled by the matrix, and are quite unfit for such minute observations. 



The small apical disc is, in general, excentral, and the madreporiform body occupies 

 the centre, covers the plates, and forms a prominence ; there are four perforated genital 

 plates, and five distinct ocular plates (fig. 2 h and fig. 2 /). The two anterior genital 

 holes are placed nearer together than the posterior pair. 



The ventral surface is slightly convex, or nearly flat; the tubercles are much larger in 

 this region, and exhibit the arrangement shown in fig. 2 i, where each tubercle rises on 

 the surface of a rounded boss and is encircled by a ring of granules (fig. 2 c). The 

 mouth-opening is excentral and nearer the anterior border, the peristome is pentagonal and 

 surrounded by five prominent tubercles which form the termination of the inter-ambulacral 

 areas (fig. 2 c). From the inter-lobular spaces ten short petaloid ambulacra proceed, and 

 these collectively form rosettes around the peristome, as shown in fig. 2 h, where this 

 structure is drawn magnified six diameters. 



The vent opens in the upper portion of the truncated posterior border in a well- 

 defined vertical area; it is oblong, and varies in size in different specimens, but is always 

 small in proportion to the size of the test. 



The periprocte is prominent, especially in the upper border, which, in some specimens, 

 overhangs the vent in a beak-shaped fashion (fig. 2 ^). 



Affinities and Differences. — This species is found in the Upper Greensand or 

 Cenomanian stage throughout the Anglo-Parisian and Mediterranean basins, and it is the 

 only form of Catojjygus hitherto collected in this stratum in England ; its characters are so 

 definite and distinct that there is no difficulty in distinguishing this species from its 

 congeners. 



Locality and Stratigraphical Position. — It has been collected from the Upper Green- 

 sand of Warminster and Chute Parm, Wiltshire ; Ilythe, Kent ; and from the junction beds 

 of Upper Greensand and Chalk-marl at Maiden Bradley, Wiltshire ; and from the Chloritic 

 Marl, near Chard, whence my best specimens were obtained. The foreign distribution of 

 this species, according to M. Cotteau, is from the Cenomanian or 20th stage of d'Orbigny, 

 the equivalent of the Upper Greensand of English authors. In France it is common at 

 Mans, Coulaines, Saint-Calais, and Condrecieux, Sarthe ; Villers, Trouville, Calvados ; 

 Havre, Seine-Inferieure ; Grace, Orne ; Vierzou, Cher; Chinon, Indre-et- Loire ; Fouvas 

 and Bel-Air, near Pvochcfort, and other localities. In Belgium in the Tourtia of Tournay ; 

 in WestphaUa at Essen on the Ruhr. 



