Vol I. Grabau — Ordovician Fossils from North China (i) 21 



upper surfaces of which all lie at the same level, or are depressed so faintly as to bo 

 scarcely noticeable. Side or body of tbe whorl at first vertical, thus making the shoulder 

 angle 90 degrees. This verticality is most marked in the last or body-whorl of the adult 

 shell, whereas in tlie young, the contour quickly becomes rounded oi? inw^ards, this 

 rounding Ijeing progressively more pronounced in the younger portion of the shell. On 

 the under or umbilical side, the inner ^vhor]s are probably depressed, though so far only 

 weathered specimens have been obtained, in which the whorls appear entirely flat. In 

 these however the outer Avhorls are quite evidently \\orn down to tlie level of the inner. 

 In a young specimen partly freed from the matrix, this depression of the inner whorls is 

 indicated. 



In an adult specimen, (Plate II, fig. 1) the greatest diameter of which is 24 mm. 

 the width of the final A\'horl (shoulder widtli) is 6.S mm. In a young specimen (pi. II. 

 figs. 2a-b) with a maximum diameter of 14 mm., the fxual whorl has a diameter of 4 mm. 



The most characteristic features of this species are: the flat surface of the spire 

 forme<l by the shoulder, the position of which is at right angles to the axis of the shell, 

 and the snbmarginal carina. The lines of growth are not sufficiently shown in any of the 

 specimens so far found to indicate whether or not there is a deep notch upon the keel 

 such as characterizes typical species of Opliileta. Nevertheless the general characters are 

 such as to make reference to the genus Ophileta most reasonable. 



Of American species of the genus known to me, the present form comes in many 

 respects near to 0. comphinata, of the Beekmantown (Lower Ordovician). It diifers 

 however from that species in the flat spire, and the sunken or depressed umbilical area, 

 which in the American form is flat, •while the spire is depressed and the A\horls concave. 

 As in the American form, the upper keel is submarginal and the sides of tjje shell flat 

 and nearly vertical, except in the lower portion, where they curve inwards in the Chinese 

 species. 



In general appearance the Chinese species is very like that descriped and figured 

 by de Verneuil as variety A, of EuompJiahcs qualteriatus Salter, in the Palseontological 

 volume of the great \\'ork on the Geology of Eussia and the Ural Mountains (p. 334, pi. 

 XXII, figs 2a, 2b,), Indeed our form might be considered conspecific with the Russian 

 form (obtained from the Ordovician rocks of St. Petersburg), which is most certainly 

 distinct from Salter's species. The two forms are very similar, exc(^pt for the absence in 

 the Russian form of the outer keel, which is distinctly shown in the Chinese species, and 

 for the fact that the shoulder angle of the Russian form is less than 90 degress. 



Horizon AND Locality: This species was collected by F. F. Mathieu, geologist 

 of the Kailan Mining Administration, in the Liangchiashan limestone at Liang-Chia- 



