R. Ether Idge, jun. — Palceontological Notes. 117 



Practically then the Micrasters of one horizon in the Chalk differ 

 from those in the preceding or succeeding horizon in a manner 

 which is suggestive rather of progressive development than of 

 simple variation. 



But there are other less apparent, yet not less actual, differences 

 between the various forms or species of Micraster. One of these 

 consists, as has been well shown by Prof. Hebert,' in the arrange- 

 ment of the granules on the petaloid portion of the dorsal ambulacra. 

 Another difference may be observed in the ornamentation of the 

 base of the test. Yet another in the number of plates impinging 

 on, or notched by, the anal opening, which varies apparently from 

 seven in the earlier species to five and sometimes four only in the 

 later forms, or species, in the English Chalk. Independently, there- 

 fore, of differences of height, length, and breadth, which vary to 

 some extent in the same species, and setting aside Micraster cor-bovis, 

 and the extreme form of M. gibbus now generally recognized as an 

 Epiaster, there would appear to be greater constant differences 

 between the Micrasters of the English Chalk than is consistent 

 with simple variation. 



Have we then indeed but two species of Micraster in the English 

 Chalk ? For myself I am inclined to the opinion that we have not 

 two species only, but several species, as many possibly as six or 

 seven. What these represent may possibly form the subject of a 

 future note. 



V. — Pal^ontological Notes. 



By R. Etheridge, jun., F.G.S. 

 (Continued from Vol. IV. N.S. p. 320.) 



1. Dentalium ingens, de Koninck, and D. ornatum, de Kon. 

 (Descrip. Animaux Foss., pp. 317 and 318, t. 22, f. 2 and 3). — 

 The first of these species has been often recorded from Scotch 

 Carboniferous rocks, but, so far as I am aware, the second is new 

 not only to Scotland, but in British Carboniferous rocks generally. 

 Specimens were forwarded to Prof. L. G. de Koninck, M.D., who 

 was kind enough to confirm my determination. Our specimens of 

 both the above species show the growth striae of the shell to have 

 been waved, like the septa of some Orthoceratites, consequently I 

 presume the anterior apertures would be similar. In Prof, de 

 Koninck's figures the strige are oblique, and the anterior aperture 

 is described as oblique. D. ingens is from the shale above the Skate- 

 raw Limestone (L. Carb. Limestone Group) at East Barns, near 

 Dunbar, and D. ornatum from shale above the Eoscobie Limestone at 

 Eoscobie. 



Collector, Mr. James Bennie. 



2. Ehynchonella or Orthis, n. sp.(?). — A very peculiar Carbon- 

 iferous Brachiopod has lately come to light ; unfortunately we have 

 only one specimen at present, and that not quite perfect about the 

 hinge. The shell in question is minute, about the size of a small 



1 Mem. Soc. Geol. de France, 2 ser. torn. v. pi. xsix. fig. 14-19. 



