294 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvm. 



short, and divided midway by a relatively" larye triangular delthyrium. 

 Transverse sections ot" the umbo near the beak show the cross section 

 of a well developed spondylium supported on a medium septum. Dorsal 

 valve about as convex as the venti'al on the umbo but the strong, 

 })road median fold makes it more strongly convex anteriorly. Cross 

 sections at the umbo show a spondylium and supporting septum very 

 much like that in the ventral valve. 



Ohservatloufi. — This species is taken as the Cambrian type of the 

 genus 8yntroj)hia, It has a spondylium in each valve supported by 

 a median septum in the same manner as in the Ordovician type of the 

 genus *S'. lateralis. Its rotiuid form, deep ventral sinus, and strong- 

 dorsal fold serve to distinguish S. rotundata from other species of the 

 genus. 



Formation and locality. — Upper Cambrian. Limestone on Wolf 

 Creek, Big Horn Mountains, 14 miles west-southwest of Sheridan, 

 Wyoming. 



SYNTROPHIA TEXANA, new species. 



CamereUa sp.? IShumard, Am. Jour. Sci., 2d ser., XXXII, 1861, p. 221. 



This ma}^ be called the plicate species of the group of forms referred 

 to Sy/d)'op/iia. It is intimatel}^ connected with the smooth forms b}' 

 a series of shells that vary from 1(1 ribs on a valve to 1. In form 

 S. texana is much like S. ahnormis; also in the cross section of its 

 spondylium. The}' dift'er in the extravagant development of the pli- 

 cations of ,6'. ahnonnis, a feature characteristic of a large series of 

 specimens. 



S. texana occurs in great numbers in one of the upper limestone 

 beds of Packsaddle Mountain. 



The average size of the larger shell is, width, S mm., length 

 6 to 7 mm. 



It is probable that this is the shell referred to by Doctor Shumard 

 as CamereUa sp. 'i He said of it — 



There are several .specimens of small brachiopod in the Texas State collecfion from 

 the Potsdam sandstf)ne of Morgan's Creek, Burnet County, which appear to belong 

 to the genus Camerdld recently created by Mr. E. Billings. Unfortunately, however, 

 they consist merely of detached and imperfect valves, too much weathered for satis- 

 factory determination and description.'^' 



Formation and JocaJlty. — Upper Cambrian. Packsaddle Mountain, 

 Llano C/Ounty, Texas. 



SYNTROPHIA TEXANA LAEVIUSCULUS, new variety. 



A variety occurs in Texas with few traces of plication in the sinus; 

 with one, two or three strong plications on the dorsal fold, or none at 

 all; it approaches S. ahnm'mis in some of its extreme forms where the 



"The Primoi'dial Zone of Texas, with descriptions of New Fossils, American Jour. 

 Sci., 2d ser., XXXII, 1861, p. 221. 



