6 



BRITISH FOSSILS. 



by the constant rotundity of its basal margin, which is tumidly rounded, 

 instead of being subangularly compressed. The ambulacral areas are 

 usually prominent, often so much so as to give a strong angularity to the 

 contour, and always narrower in proportion to the interambulacrals than 

 in the other species. The anus is inferior, strongly and tumidly promi- 

 nent and marginated, and always either round or broader than long, a 

 character never present in its congeners. The whole surface above and 

 below is rough with granulations, interspersed with the primary tubercles, 

 which are nearly equal on the ventral and dorsal surfaces. The miliary 

 granulation is quite as strong above as below, and strikingly contrasts 

 with the apparent smoothness of the surface which distinguishes albo- 

 galerus and suhrotundus. The margins of the mouth are usually 

 tumid, and the avenues of pores when advancing to it, do not become so 

 closely ranked as in the species just named. Galerites ahhreviatus 

 appears to be characteristic of tiie upper chalk. 



3. G. suhrotundus. — Although this name was given by Agassiz to a 

 single English specimen, and previously by Mantell to a questionable 

 cast, I prefer retaining it to using that of vulgaris, adopted, after 

 Lamarck, by Agassiz and Desor, for what I regard as perhaps the more 

 ordinary form of the same species. I reject the latter name, since under 

 it so many good figures of the last species mentioned have been pub- 

 lished, and adopt suhrotundus, since one of its forms has been ex- 

 cellently figured under that name by Desor, and since it has not 

 been applied to any other species. It is a common English Galerite, 

 and apparently is chiefly confined to a lower geological horizon 

 than that of the two preceding species, being chiefly character- 

 istic of the hard or lower chalk. In form, it varies from a depressed 

 spheroid with a truncated base to nearly globular ; the anus is always 

 vertically elliptical, not rostrated nor tumid, and is placed on, or in 

 some occasional specimens, above the margin. The mouth is central. 

 The margins of the sides are always more or less rounded. The 

 spiniferous tubercles of the base are conspicuously larger than those of ' 

 the dorsal surface, but all are smaller and more numerous than those 

 of alhogalerus. The spines of the lower surface are smaller and 

 different. The pairs of pores fall into close ranks near the mouth, but 

 are more oblique, and the series are not so directly under each other as 

 in alhogalerus. The Galerites globulus of Desor, founded on a single 

 white-chalk English specimen, is a not rare but exceptional dwarf variety, 

 and Globator yiucleus of Agassiz is something too like an abnormality 

 of this species. Galerites Leskii (Desor), is another variety. 



4. Galerites castanea, with which I unite Pyrina depressa and Galerites 

 IcBvis, possibly also Galerites Orbignyana (founded on a single specimen 

 from Touraine) may fall in here. But of this fourth species I have fully 

 treated in the account of Galerites castanea. 



