igi 



very strongly swollen, and the \entral valve is provided with a shallow but 

 rather wide sinus which begins at the middle of the shell. Conse([uentl\- the 

 anterior margin of the shell is convexely deflected in the ventral valve, while 

 in consequence it is concaveh' deflected in the dorsal. If, therefore, the 

 Chinese specimens at the writer's disposal are to be compared with 

 those adult examples there may really e.xist rather remarkable apparent 

 differences between them. The largest specimens from the province of 

 Kwang-hsi, however, are comparable with some of them. 



There are also smaller or younger examples^' illustrated by many authors 

 which are comparable with these smaller examples from China. In such 

 younger specimens the sinus is less conspicuously develo[)ed, or even not 

 developed at all, the front margin then being nearly straight. " The speci- 

 mens," says KiXDLE, " vary widely among themselves with reference to the 

 depth of the sinus at the front, but this variation is mainly a developmental 

 feature, the sinus being slightly indicated in the younger shells, and very 

 deep in mature .specimens."-* There is even one specimen among the ex- 

 amples hitherto described, namely one Russian fossil described by Tscheknv- 

 SCHEW^' in which the ventral valve is somewhat deeper than its opposite. 



The difference of the Chinese specimens from the typical forms is thus 

 of rather an unimportant nature, and does not militate against identifying the 

 former with Dahiiaiiclld sti iatula. 



This species had been most popularly known as an 0> tliis until it was 

 removed to the genus SchizopJtoi ia by (xiRrv.^* Very recently OuiRiNrr, in his 

 monographic stud}-, came to place it in the genus Dal maiii lliu These two 

 last genera are regarded by H.VLi, and Cl.vkke as subgenera of Orthi^?'' Ac- 

 cording to ScuucHEKT,''* however, these three genera are far more widely 



1) Schnlk; — op. cit., pi. XX.WIII., fig.s. Ih, i, k; — Hall: — op. cit., pi. 15, figs. 2a, b, c; — 

 D.^VIDSON: — op. cit.. pi. .XVII., figs. 7, 7a; — TSCHKRN VSCHLW : - - Op. cit., pi. III., fig. iS; — 

 Kindle:— op. cit., pi. I., fig. 4 ; pi. II., Fig. la; — Manuys : --op. cit., pi. I.\., figs. 4a, b. 



2) KlNHLE: — op. cit., p. 21, 



3) TSCHEKNVSCHEW: — op. cit., pi. III., fig. l8. 



4) GiKTv: — Twenteeth Ann. Kept. U. S. Geol. Survey, Pt. 2, p. 39. Cited aftt-r Kindle, op. 

 cit., igog. 



5) ZiTTEL: — Grudziige dtr Palaeontologie, I. .\bt. Invertebrata. p. 275. igio. 



6) Eastman: — Text-Book of Paleontology, vol. I., 1913. 



