CAMBRIAN FA UNAS OF CHINA— WALCOTT. 19 



Transverse section rounded sal)triaiio-ular, transverse, and slig-htl}' 

 concave toward the center on the dorsal side, rounded at the lateral 

 angles, highlj' arched on the ventral side, with the ventral angle 

 broadly rounded. Dorsal face of the lateral angles rounded, with a 

 shallow depression, with rounded lateral slopes, a little more than 

 one-third the width of the face. Ventral face strongl\' and regularly 

 convex transversel3% and without any ventral angle. Aperture, as 

 far as known, transverse, at right angles to the axis of the shell. 

 Operculum unknown. Shell of moderate thickness and made up 

 apparently of several hn'crs or lamelh^. 



Surface of the shell concentrically or transversely linel}^ striated; 

 a few longitudinal stride may be seen bv turning the specimen in the 

 light.- 



The largest specimen, which is broken off at the apical end, has a 

 length of 9 nnn., with a Avidth on the dorsal side at the larger end of 

 2 mm.; a specimen with a diameter of 3 mm. on the dorsal face has 

 a dorso- ventral diameter of 2 mm. 



What appears to be a ti-ansverse septum occurs in one of the shells 

 about 9 mm. from the apical end. 



The elongate form of the tube and the shallow groove on the 

 center of the dorsal face are not unlike IlyoHtJics commvnis euiiiionsl 

 Ford." The two species, however, ditier in the outline of the trans- 

 verse section and in the more rapidly expanding tube of Oiihotheca 

 cyrene. There is a number of species from the Swedish Cambrian, 

 illustrated by Holm, that have the central depression on the dorsal 

 face. Of these (Jrthotliecd ((jfi)iis Holm is most nearly related to O. 

 cyrene. 



Foriiiation and loadify. — Upper Cambrian, upper portion of Chao 

 Mi Tion formation; Chao ]Mi Tien and 2.7 miles southwest of Yen 

 Chuang, Hsin Tai, Shangtung, China. 



Collected by Eliot Blackwelder, of the Carnegie Institution of 

 Washington P^xpedition to China. 



ORTHOTHECA CYRENE DRYAS, new variety. 



This variet}' is characterized by having a broader, more shallow fur- 

 row on the dorsal face; otherwise it appears to be identical with (>. 

 cyrene. On some specimens the shallow groove is scarcely percepti- 

 ble, the face being practical 1}^ transverse and smooth. 



Forniatlon and local !ty. — Middle Cambrian, central portion of Chang 

 Hsia formation; 2 miles south of Yen Chuang, Hsin Tai, Shangtung, 

 China. 



Collected by Eliot Blackwelder, of the Carnegie Institution of 

 Washington Expedition to China. 



a Tenth Ann. Kept. U. S. Geol. Survey, 1890, pi. lxxvii, lig. 4A. 



