NO. 1152. CAMBRIAN Bit A CHIOPODA— WALCOTT. 419 



A single specimen donbtfnlly referred to this species from near 

 Montevallo, (Jeorgia, shows a surface over a small i)ortion of its area, 

 much like that of 0. {L.) ella. Jt is too doubtful to refer to 0. [L.) eUa. 

 This s])ecies has quite a vertical range as it occurs in the Kome forma- 

 tion and in the subjacent Coosa shales. Its range of variation is con- 

 siderable; some of the Coosa shale specimens associated with the Mid- 

 dle Cambrian fauna are very much like 0. (L.) lamborni from the 

 Kogersville shale of Tennessee. 



I take i)leasure in naming this species in honor of Mr. Bailej^ Willis, 

 geologist, who for a considerable time had charge of the work in that 

 region where these specimens were collected by Dr. Cooper Curtice. 



Formation and locality. — Middle Cambrian, Kome formation; both 

 in shales and calcareous sandstones. Copper liidge, 11 miles northwest 

 of Knoxville; 4 miles north-northeast of Knoxville, along First Creek 

 Gaj); also 3i miles southwest of Rogersville, Tennessee; "> miles north 

 of Cave Spring, Georgia, in shales beneath the limestone; doubtfully 

 in shale one-fourth mile west of hotel at Montevallo, Georgia; Coosa 

 shales of Coosa Valley, on line of Cowau Creek, Cherokee County, 

 Alabama. 



Types.— ^oa. 27343-G, U.S.N.M. 



OBOLUS (LINGULELLAj ZETUS, new species. 



This is a small shell that has somewhat the general form of 0. (L.) 

 lamborni. It differs, however, in being more transverse across the 

 front, and in having a broad, shallow dexjression in the dorsal valve. 

 It occurs at a higher horizon than 0. (L.) chuarensis, 0. [L.) ciiglijphus, 

 and 0. (//.) lineolatuH of the upper beds of the Tonto sandstone. It has 

 more the form of the true Obolus than those species, but its shell is 

 relatively thin and marked by tine radiating striie. All of its essen- 

 tial characters are well shown by the tigures illustrating the species. 



Formation and locality. — Upper Cambrian, shaly sandstone in the 

 upper beds of the Tonto formation, at the head of Nunkoweap valley, 

 Grand Canyon of the Colorado, Arizona. 



Type.—^o. 27347, U.S.N.M. 



EXPLANATION OF PLATES. 



[The letters ou the plates refer to the parts as iudicated herewith.] 

 Plate XX VL 



ij. Umbonal 

 h. Central, 

 t. Transmedian. 

 j. Anterior laterals. 

 k. Middle laterals. 

 I. Outside laterals. 

 p. Pedicle groove. 

 a. Central lalenil H|)ace. 

 a'. Outer lateral space. 



/. Flexure lines. 

 vg. Vascular sinus. 

 ps. Parietal band. 

 X. Heart-shaped cavity. 

 o. Scar-like depressions in heart -shaped 



cavity. 

 «. Median septum and ridge. 

 d. OutliiK! in liuart-sliaiH^d cavity, showing 

 a stage in the growth of the cavity. 



