UPPEE TRIASSIC SPECIES, 101 



small abruptly-pointed apices scarcely projecting above the hinge and turned 

 slightly forward. Surface marked off, as it were, into more or less wide, 

 irregular, flat radiating costse, by much narrower or merely linear furrows, 

 the ribs themselves being sometimes also more or less subdivided by much 

 finer furrows; ribs often obsolete near the hinge, both before and behind the 

 beaks, but sometimes one or both of these spaces are occupied by fine irregu- 

 lar costse ; a few very faint concentric marks of growth also usually occur 

 near the beaks. 



Length of large specimens, apparently about 2.30 inches; height, about 

 1.60 inches. 



Although this shell seems to have been quite abundant, none of the 

 specimens contained in the collection show the entire outline, though its 

 general form can be pretty nearly inferred from the faint undulations of 

 growth. It is possible that a comparison of specimens might show this shell 

 to be distinct, but I have been unable to find any greater differences, even 

 in the most unimportant details, between these specimens and the figures of 

 the European form, than I observe among the specimens themselves, and 

 between the figures of H. Lommeli, published by different authors. 



I see Professor Mojsisovics refers Ilalobia Lommeli of Wissmann, and 

 II. duhia, Gabb, to his newly-proposed genus Daonella. I am not very well 

 acquainted with the type-species of Bronn's genus Ilalobia; his figured speci- 

 men, as well as those illustrated by Professor Mojsisovics, being quite im- 

 perfect. If I can be permitted to judge, however, from the figures of sev- 

 eral other species referred to Ilalobia and Daonella by Professor Mojsisovics, 

 there would seem to be such a series of intermediate gradations between 

 these two groups as to leave the impression that they are hardly more than 

 subgenerically distinct, if even that. The only difference seems to be that in 

 the typical species oi Daonella (D. Moussoni) the lateral margins round into the 

 straight dorsal border, while in the species referred by Professor Mojsisovics 

 to Ealobia, they meet the straight dorsal edge at more or less obtuse angles; 

 and on the anterior side the cardinal margin is compressed, or has an oblique 

 furrow, indicating a slight tendenc}^ to form an obscure anterior auricle, 

 defined by the faintest possible indication of a marginal sinus. With these 

 exceptions, the diagnoses of the two groups are precisely the same. 



