Reviews — Prof. Morse — An Early Stage of Acmcea. 41 



of ten fossil crinoids, ranging from Lower Ordovician to Eocene, were 

 also examined, but, with one exception, showed a very small 

 percentage ( - 8 to 2 - 56) of magnesium carbonate. The alteration 

 is ascribed mainly to infiltration by calcium carbonate and other 

 constituents, wliich would naturally lower the proportion of 

 magnesium carbonate. The original suggestion, therefore, that 

 crinoids might play an important part in the formation of magnesian 

 limestones is far from being supported. Nor is it supported by the 

 sole exception, for this was a stem of the common Lily Encrinite 

 from the Muschelkalk ; and the reason that this had no less than 

 20 - 23 per cent of magnesium carbonate is presumably that it came 

 from one of the many Muschelkalk limestones that have been 

 dolomitized. Even so the proportion of magnesium carbonate does 

 not come near that which obtains in true dolomite. 



VII. — Professor E. S. Mouse on an Early Stage of Acmjea. 



PROFESSOR EDWARD S. MORSE'S paper (Proc. Boston 

 Society of Natural History, February, 1910) on "An Early 

 Stage of Acmeea", though delayed in coming into our hands, 

 deserves even a late appreciation. Contributions to our knowledge of 

 the phylogeny of the Mollusca are exceedingly desirable, and we 

 wish students of this phylum would spare more time from systematic 

 conchology to the study of such problems as Mr. Morse deals with in 

 his paper. The author, after a study of two species of Acmcea, in 

 which (in one at least) no trace of a coiled Nautiloid apex was found 

 in the embryonic stage (though such a coiled apex has been found 

 in the early stages of other Docoglossa), proceeds to review some of 

 the evidence (palaeontological, embryological, and anatomical) that 

 suggests that the Docoglossa are actually primitive Gastropoda. It 

 is plain, of course, that all the members of the sub-order (Lepeta, 

 Pilidium, Helcion, etc.) must be examined before we attempt to 

 formulate any final statement as to the evolutionary status of the 

 Docoglossa, and in the meantime such evidence as Mr. Morse is 

 able to produce is most valuable, if not actually sufficient to upset 

 the belief that the Docoglossa are not entirely primitive in their 

 structure. 



VIII. — Brief Notices. 

 1. In a paper recently published in the Smithsonian Miscellaneous 

 Collections (vol. lx, No. 21) J. W. Gedley records the occurrence of 

 a bone of a camel associated with remains of the mammoth and bison, 

 from a locality in the Yukon Territory, Alaska, some distance within 

 the Arctic Circle. Although, as is weil known, the Bactrian Camel 

 can endure extreme cold, no remains of any member of this group 

 have hitherto been found nearly so far north. 



2. Chalk of Gingin, Western Australia. — Mr. R. Etheridge has 

 issued as Bulletin No. 55 (1913) of the Geological Survey of Western 

 Australia a description of the fossils of the Gingin Chalk. The 

 fauna shows a striking similarity to the uppermost White Chalk of 

 England, with Magas and Trigonosemus. In Bulletins Nos. 36 (1910) 



