442 CAMBRIAN BRACHIOPODA. 



Schnidtia Volborth, Hall and Clarke, 1892, Nat. Hist. New York, Palseontology, vol. 8, pt. 1, p. 83. (Discussed.) 

 Obolus (Schmidtia) (Volborth), Mickwitz, 1896, M6m. Acad. imp. sci. St.-P6tersbourg, 8th ser., vol. 4, No. 2, p. 158. 



(Described and discussed in German; see below for translation.) 

 Obolus (Schmidtia) (Volborth), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 683. (Characterized.) 

 Obolus (Schviidtia) (Volborth), Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 144. 



(Classification of genus.) 



The original description by Mickwitz follows: 



The subgenus Schmidtia, out of all the subgenera of Eichwald's genus, is most closely related to the subgenus Eu- 

 obolus. Some species of that subgenus, especially 0. celatus and to a less degree 0. crassus, show in their general appear- 

 ance so much resemblance to 0. apollinis that they might pass for miniature models of it. The other two species, on 

 the contrary, depart from the typical species in the form of the valves and in the shape of the area; 0. obtusus, in outline 

 and in the flatness of its valves, rather resembles Lingula, while 0. acuminatus has a very peculiar form, differing from 

 all Oboli, and due in part to the peculiar conformation of the apex of the beak. 



The main arguments for establishing a special subgenus Schmidtia alongside of the subgenus EuoboliLS, aside from 

 the extraordinary smallness of the valves, are: the absence of radial striation of the surface of the valve; the absence of 

 longitudinal striation from the slope of the thickened posterior part of the valve, as well as of the posterior edge of the 

 central pit; the invariably more uniform thickening of the valves, manifested in this, ainong other things, that the 

 pleuroccelic parts of the valves differ in nothing from the frontal and side edges; the fact that the area of the large valve 

 is broken in the plane of the pedicle fiu'row; the pit-shaped depression of the splanchnocoelic part of the area of the 

 small valve; the pestle-shaped form of the central pit; the recession of the horn-shaped projections and of the sinus of 

 the small valve, while the median ridge simultaneously predominates. A fiu-ther difference seems to exist in the 

 different conformation of the inward-radiating secondary vessels, which in some species of the subgenus Schmidtia ai'e 

 variously ramified, whereas in the subgenus Euobolus, so far as can be seen, they ai-e more rectilinear and less branched. 

 Still the knowledge of these organs in the species of the two subgenera is as yet too imperfect to permit a definite 

 statement. 



Type. — ScJimidtia celata Volborth. - ; 



Ohservations. — The reasons stated by Mckwitz [1896, p. 158] for establishing Schmidtia as 

 a subgenus of Oholus are essentially those that differentiate it from Lingulella. The species of 

 the latter subgenus are radially striated and the shells are uniformly thinner. So far as IcQOwn, 

 all of the species of ScJimidtia are those described by Mickwitz from the Oholus beds of Russia. 

 In order to place before the student full details of the species, I have had drawings made from 

 the original specimens received from Mickwitz, and have also introduced the greater portion of his 

 detailed descriptions. In order also that there may be a reference in this monograph to the 

 varieties Mickwitz has determined, these are included in the synonymy of the different species 

 referred to ScJimidtia. 



The subgeneric name was given in honor of Dr. Fr. Schmidt, of St. Petersburg, Russia. 



Obolus (Schmidtia) acuminatus Mickwitz. 

 Plate XIV, figures 2, 2a-c. 



Obolus (Schmidtia) acuminatus Mickwitz, 1896, M^m. Acad. imp. sci. St.-P6tersbourg, 8th ser., vol. 4, No. 2, pp. 179- 

 183, PI. II, figs. 39 and 40. (Described and discussed in German as a new species; see below for translation.) 



Obolus (Schmidtia) acuminatus alatus Mickwitz, 1896, idem, pp. 183-184, PI. II, figs. 41 and 42. (Described and dis- 

 cussed in German as a new variety.) 



Obolus (Schmidtia) acuminatus humeralus Mickwitz, 1896, idem, pp. 184-186, PI. II, figs. 43 and 44. (Described and 

 discussed in German as a new variety.) 



Obolus (Schviidtia) acuminatus subtriangularis Mickwitz, 1896, idem, pp. 186-187, PL II, figs. 45 and 46. (Described 

 and discussed in German as a new variety.) 



The original description by Mickwitz follows : 



This remarkable species comprises, as the preceding, a number of forms essentially deviating from one another 

 (especially in outline), whose unity can be safely asserted only by the agreement of certain characters important for 

 the distinction of different species of the subgenus Schmidtia. To these belong, in the fijrst rank, the peculiarly devel- 

 oped beak, with the aberrantly placed indications of a pseudo-area, which stands in a ceitain opposition to that of 

 0. obtusus. The latter shows, as we have seen, this part of the shell fiat, obliquely truncated, and the traces of a 

 pseudo-area far removed from the peduncular groove. With 0. acuminatus, on the contrary, the beak is highly arched, 

 inwardly bent, and the traces of a pseudo-area Coincide with the borders of the peduncular groove. 



Diagnosis: Shells small; large shell (ventral valve) strongly arched, small shell (dorsal valve) more weakly. 

 Greatest height of both shells directed more toward the beak. Outline oval. Beak of the large shell high, pointed, 

 falling off steeply toward the tip of the beak and the umbonal borders. Tip of the beak bent inward. Anterior border 



