422 



PBOE. P. 31. DUNCAN ON ECHEN T OIDEA 



authors, and it is especial!} 7 mentioned here in order to bring it into 

 relation with a Micraster from the Indian Nunnnulitic deposits. 



The height and general tumidity of the test and the short ambu- 

 lacra separate the Australian form from all the Cretaceous species 

 of the well-known genus ; but in these details there is an evident 

 alliance with Micraster tumulus, Dune. & Sladen, from the Khirthar 

 or true j^ummulitic limestone of Western Sind (Pal. Ind. ser. xiv. 

 pi. iii. p. 189, 1884). This species, from older Tertiaries than those 

 of Australia, has slightly longer and wider ambulacra than the 

 other, and in both the evidences of a subanal fasciole are not 

 satisfactory. The posterior groove leading from the margin to the 

 periproct is more decided in the Australian form, and the whole of 

 the posterior surface is wider in the Australian form than in the 

 Indian. The British Museum specimen is 50 millim. high, 62 millim. 

 long, 51 millim. broad, and it has traces of a subanal fasciole (not a 

 lateral one, as stated in the former paper). 



19. Mabetia axomala, Dune. op. tit. p. 52, pi. iv. figs. 1-4. 



The abnormality in this species is the presence of a more or less 

 discontinuous fasciole just above the ambitus. Since the description 

 of the species, A. Agassiz has found a corresponding fasciole in a 

 recent species. 



20. Megalastee compeesstjs, Dune. op. cit. p. 62. 



The species is retained provisionally, for the ornamentation has 

 almost all disappeared and the possibility of its turning out to be 

 a Pericosmus is considerable, as will be understood after reading 

 M'Coy s observations on that genus. But it must be admitted that 

 the specimen in the British Museum does not show the least trace 

 of fascioles, and that there are clear specific distinctions between 

 it and any species of Pericosmus, leaving out the consideration 

 of the fascioles. The length of the specimen (E 296, B.M.) is 

 5 inches, the width 4*75 inches, height 24 inches. The apical 

 system is more or less deficient, but the radial plates are small, 

 obscurely quadrangular and longer than wide ; the tentacular pore 

 is very large, the poriferous plates of the ambulacra, near the radial 

 plates, are small and perforated by pairs of minute foramina ; and in 

 the posterior lateral ambulacra, at about the sixth plate, the plates 

 dip down into the ambulacral groove. At a little distance from the 

 small plates the others become large, low and broad, and the inner 

 pore is large and slightly elongate, although, on the whole, circular 

 in outline, and the outer pore is very long and most open externally. 

 There is no groove between the pores of a pair, and the pairs are 

 separated by very distinct and ornamented costse. The anterior 

 ambulacral pores are all small and circular and become very distant 

 halfway down the very deep and broad groove. The postero- 

 lateral petals are slightly wavy, long, narrow, and deep ; they are in 

 a narrow depression of the test, so that the poriferous zone does not 

 come up to the level of the test, but is on the flank of the depression. 



