FROM THE CORALLINE OOLITE. 349 



and occupies the centre of the disc ; it appears to cover the genital plates (fig. 2 e), and 

 the four genital holes are large oblique slits, which extend into the inter-ambulacral areas 

 (fig. 2 e). 



The base is nearly flat at the sides, and slightly concave towards the mouth-opening 

 (fig. 2 (5). In large, well-developed specimens, the inter-ambulacral areas are a little 

 prominent, and the course of the ambulacra is marked by corresponding depressions in 

 the test ; the poriferous zones are so feebly shown, that the pores can only be seen with a 

 lens. 



The mouth-opening is moderately large for a nucleolite ; it is situated in a depression 

 opposite the apical disc, and is nearer the anterior than the posterior border (fig. 2 b) ; 

 the peristome is pentagonal, and each angle of the pentagon corresponds to an ambulacral 

 area ; the areas form inconsiderable petaloidal expansions as they radiate from the peristome, 

 and the pores are crowded close together in the vicinity of the mouth- opening. The anal 

 valley forms one of the distinctive characters of this species (fig. 2 «) ; it is of an ovate or 

 lanceolate form, with a blunt apex ; in some specimens it appears as if a portion 

 of the inter-ambulacrum had been drilled out for the passage of the intestine; in 

 some individuals it extends only half the distance between the margin and the vertex, whilst 

 in others it reaches two thirds the length ; in all the specimens I have examined, an 

 undepressed portion of test separates the apical disc from the upper border of the anal 

 valley ; inferiorly, the valley forms a considerable sulcus, grooves the centre of the area, 

 dividing its posterior border, and producing the cordate or bilobed form this species 

 assumes (fig. 2 a, b). 



Affinities and differences. — I have already stated that E. scutatus was formerly 

 considered by English naturahsts to be a variety of E. chnictilaris, Lhwyd, and as such its 

 history is more or less connected with that species. Were a student, therefore, to endeavour 

 to unravel its synonyms from the books alone, he certainly would be puzzled in his search, 

 as the critical remarks on E. scutatus have more frequently been made on book-statements 

 than from an examination of specimens. If, however, a comparison be made between a 

 series of E. clunicularis, Lhwyd, from the Cornbrash, with a corresponding series of E. 

 scutatus, Lamk., from the Calcareous Grit, all doubts will be removed from the mind of the 

 observer as to the specific difierences existing between these species ; and in default of such 

 specimens, a careful study of Mr. Bone's most excellent figures in our Plates XXIV and 

 XXVI, with the ample magnified details he has given therein, will afford sufficient 

 evidence for our conclusion. 



E. scutatus, Lamk., so nearly resembles E. dimidiatus, Phil., that the latter has by 

 many been considered to be a variety of the former ; this point, however, will be more properly 

 discussed in the section devoted to the description of E. dimidiatus, Phil. 



These are the only English nucleolites which at all resemble E. scutatus. Between all 

 the other older species and this Corallian form the distinctions are numerous and self- 



