ADDENDA. 



MiCRASTER coH-TESTUDiNARiUM, Goldfuss. PI. LXXVI, fig. 1 a—f, and fig, 2 a — e. 



Spatangds cor-testudinarium, Ooldfuss. Petref. German., p. 156, pi. xlviii, fig. 5, 



1826. 

 MiCRASTER — Agassis. Prod. Monog. des radiaires ; Mem. Soc. des 



Sc. Nat. de Neuchatel, t. i, p. 184, 1835. 



— — Roemer. Nord-deiitschen Kreidgebirges, p. 33, 1840. 



— — Morris. Catal. of British Fossils, p. 54, 1843. 



— — Hebert. Foss. de la Craie du Meudon Mem. Soc. 



Geo), de France, 2 ser.,t. v, pi. xxix, fig. 18, 1855. 



— — Hvans. Proc. Geol. Assoc, vol. V, No. 4, pl.ii, 1877. 



Diagnosis. — Test cordiform, greatest width at the junction of the anterior with the 

 middle third of the ambitus, posterior two-thirds tapering to a very narrow posterior 

 border. Upper surface convex, more or less elevated, anterior half obliquely declining 

 towards the an teal sulcus, posterior half often developing a prominent central ridge 

 extending from the disc to the periprocte ; summit central ; surface of the plates covered 

 with small tubercles. Under surface convex ; plates covered with large tubercles ; mouth- 

 opening at a distance from the border, near the junction of the first with the second 

 fourth of the antero-posterior diameter of the base. Peristome transversely oval, with a 

 thick, projecting lower lip. 



Dimensions. — Height one inch and a half; length two inches and one tenth; width 

 two inches and one tenth. 



Description. — It is difficult to unravel the synonymy of this species, seeing that it 

 has been confused by some with Micraster brevis, and by others with Epiaster gibbus ; so 

 that unless we had the specimens referred to for special examination and comparison, it 

 woidd be impossible to determine the species indicated in some published lists. I have 

 limited, therefore, my synonyms to the few examples I happen to know. 



Goldfuss figured, as the type of his species, a large globular variety, but did not at 

 the same time indicate that it was an exceptional example, and for this reason English 

 geologists were long doubtful whether our Chalk contained the German Micraster 

 cor-testudinarium, Goldf. In consequence of considerable importance having lately been 

 attached to this species by Continental geologists in their classification of the Cretaceous. 



