OBOLID^. 383 



Diagnosis: Shells flat, outline oval to rounded, tip of beak of the large valve somewhat drawn forward and some- 

 what curved inward. Concentric and radial striation faint and irregular, the latter somewhat unpronounced, at times 

 lost in an irregularly rent shell surface, but always recognizable at the posterior edges of the shell. Front and side 

 edges thin, sharp, brittle, lying in the same plane as the thickened edges of the beak. Area in the median line some- 

 what concave; pedicle tuiTow distinctly developed, slightly tapering toward the apex of the beak. Lines of folding 

 of the area lamellae slightly concave to the median line of the valve and converging into the apex of the beak. The 

 thickening of the posterior half of the valve is massive; the slope of the thickening down to the middle of the valve, 

 in the large valve, shows longitudinal striae and transverse traces of the secondaiy vessels. The traces of the main 

 vessels in both valves are broad and flat and on both sides marked at the bottom by narrow grooves. The grooves of 

 the secondary vessels, radiating into the interior of the valves, are rectilinear, unbranched, and at right angles to the 

 grooves of the main vessels. The central pit has the shape of the conventional heart, opens into the brachiocoele through 

 the median furrow and shows longitudinal strias at its posterior edge. The muscular attachments of the combined 

 outside lateral and central muscles of the large valve are drawn out into furrows toward the beak, which extend beyond 

 the posterior edge of the central pit. 



Observations: The defective condition of the shells leaves many characters uncertain. Thus even in relatively 

 well-preserved specimens the edges of the shells are broken off and show neither the anterior course of the main ves- 

 sels nor the mouths of the secondary vessels where they enter the peripheral vascular canal. 



The scars of the anterior lateral muscles of the small valve, which, owing to their position far forward, are also 

 for the most part broken off with the edge of the valve, were seen in three specimens. 



In the typical form there seems to be a certain correlation between form, shell surface, and internal configuration, 

 but this correlation is not carried out very rigorously. The oval forms have the tip of the beak drawn somewhat farther 

 forward; the radial striation in them is for the most part less pronounced, while the concentric striation is stronger 

 and more roughly engraved. At the same time the shell surface is duller and lacks the strong varnish-like gloss which 

 is peculiar to the Oboli. To this external condition coiTesponds a less thickening of the posterior part of the shell, 

 and as a consequence a less pronounced development of all the characters connected with the thickening, such as 

 septa, ridges, central pit, etc. The internal marks of the last-named specimens are all developed to a recognizable 

 degree, but they lack relief. 



Quite different is the case with the rounder forms. The shell surface is smoother and glossier, the concentric and 

 radial striation more alike, though the latter is always fainter, and at times is overpowered by the beginnings of an 

 irregular cracking of the surface, which is fully developed in 0. apollinis ingricus. At the same time the internal con- 

 figuration shows a plasticity often bordering on the monstrous. 



******* 



To 0. apollinis in the narrower sense belong most of the forms described by earlier authors, in particular 0. apol- 

 linis Eichwald [1829, p. 274, PI. IV, figs. 5a-b], Ungula ovata Pander [1830, p. 59, PI. Ill, fig. 23] (while the valve 

 figured by the same author in figs. 6a-b, PI. XXVIII, belongs to a Schmidtia), 0. ingricus von Leuchtenberg [1843, 

 p. 16, PI. II, figs. 7-8], 0. apollinis de Verneuil [1845, p. 290, PI. XIX, fig. 3c], Aulonotrcta polita Kutorga [1848, p. 

 278, PL VII, figs. 10a, a', c?, d?, e?]; the other forms of Kutorga, so far as they may be recognized, belong to the varieties 

 of Eichwald's species. 



The specific name is derived from Apollo, the name Oiolus afoUinis signifying "a coia of 

 ApoUo." 



Formation and locality. « — Upper Cambrian: (395f) Oholus conglomerate throughout the east Baltic region; 

 (336c) Oholus sandstone at Reval; (395) Oholus sandstone at Joa, near Jegelecht, 12 miles (19.3 km.) east of Reval; 

 (395b) Oholus sandstone at Ilgast; (9d) Oholus sandstone at Jaggowal, about 20 miles (32.2 km.) east-southeast of 

 Reval; (336b) Oholus sandstone on Odensholm Island, about 55 miles (88.6 km.) west of Reval; (336m) Oholus sand- 

 stope at Baltischport, about 30 miles (48 km.) west of Reval; (336t) Oholus sandstone at Wiems, 5 miles (8 km.) north- 

 northeast of Reval; and (336s) Oholus sandstone at Narwa; all in the Government of Esthonia, Russia. 



(395z) Oholus sandstone at Jamburg on Louga (Luga) River; (336a) Oholus sandstone at Podolova (Putalova?) on 

 Ijora (Ischora) River; (336u) Oholus sandstone on the bank of Louga (Luga) River, southwest of St. Petersburg; (336k) 

 Oholus sandstone on Volkhof (Wolchow) River; (3361) Oholus sandstone on the bank of Sjass (Sias) River, near Lake 

 Ladoga; all in the Government of St. Petersburg, Russia. 



(336r) Oholus sandstone in the entire region between Volkhof (Wolchow) and Sjass (Sias) rivers on the east and 

 Baltischport on the west. Governments of Novgorod, St. Petersburg, and Esthonia, Russia. 



(311w) Drift bowlder of Oholus sandstone [Wiman, 1902, p. 68], Mariehamn, Aland Island, Finland, Russia. 



(386c) Drift bowlder found near Lyck, East Prussia; and (386cl) drift bowlder found near Danzig, West Prussia; 

 both in Germany. 



(321, 321a-d, and 321o) Drift bowlders of Oholus sandstone, Nos. 1-23, and 25-29 [Wiman, 1902, p. 68], on Fanton 

 Island, parish of Borstil, Province of Stockholm; (3901) Oholus conglomerate at Klittberget, in Dalarne, Province 

 of Kopparberg; (9e) Sandstone in the Oholus conglomerate at Boda, north of Rattvik, Dalarne; (311v [Wiman, 1902, 



a The collections of the United States National Museum contain specimens of Obolus apollinis from Localities 9d, 9e, 336s, 395, 395b, and 

 B95z. The other localities mentioned are taken from the references given in the synonymy. The authority for each locality cited will be 

 Ibund in the list of localities, pp. 161-291. 



