410 VROVEEDINliS OF THE NATIONAL MUSEUM. vol.xxi. 



OBOLUS (LINGOLELLA) OWENI, new species. 



General form ovate, with tbe ventral valve obtusely acuminate, and 

 the dorsal valve more broadly rounded posteriorly; valves ajipear to 

 have been moderately (jonvex, as far as can be determined from the 

 flattened specimen in the shaly sandstones. Surface of shell marked 

 by concentric lines and stri.c of j?rowth and indistinct radiating stria'. 

 There are n» traces of tlie interior markinj^s observed. Tlie shell is of 

 medium thickness; none of the specimens show how it was built up, 

 further than there weie oblique lamella' attached to the outer layer in 

 the anterior portion of the valve. The largest ventral valve from Gib- 

 raltar Blulf has a length of 10.5 mm.; width, about 12 mm.; an asso- 

 ciated dorsal valve 14 mm. in length, has a width of 11 mm. as it occurs 

 flattened on the surface of the sandstone; a smaller shell referred to 

 this species from Osceola Mills averages from to 8 mm. in length. 



As shown in the cast of an interior of a shell, the area is rather long 

 and divided midway by a sharp i»edicle furrow; the flexure lines are 

 situated about midway between the cast of the pedicle furrow and the 

 lateral margin. The area formed a thin shelf between the pedicle 

 groove and the lateral margins, the undercut extending far back under 

 the area. 



One cast of the interior of a ventral valve shows a slight trace of the 

 visceral area. In a cast of a dorsal valve both the central and anterior 

 lateral muscle scars are somewhat indistinctly ])reserved. 



Observations. — This species is most nearly related to 0. (L.) ampins. 

 It diflers, "as far as can be determined from the material for compari- 

 son, in being less elongate and in the position of the central and inte- 

 rior lateral muscle scars in the dorsal valve. 



The species differs strongly from (). (L.) stoneaniis in its surface mark- 

 ings, although the outline of the valves is almost the same in the two 

 species. 



Formation and locality. — Upper Cambrian, (Gibraltar Bluff, near Lodi, 

 Prairie du Sac, and Osceola Mills, Wisconsin. 



Types.— ^08. 27329-30, U.S.N.M. 



OBOLUS (LINGULELLA) PHAON, new species. 



General form ovate, with the ventral valve subacuminate, and the 

 dorsal broadly ovate ; valves of moderate convexity; (mter surface of 

 the shell nuirked by fine concentric lines and stria-; of growth, and very 

 tine, more or less interrupted radiating striae; the interior surface, as 

 seen in casts, is more or less marked by rather large papilhe arranged 

 in concentric lines, the i)apillie corresimnding to the pits or puncta^ on 

 the inner surface of the shell. Judging from the casts, which show very 

 deeply impressed vascular and other markings, the shell must have 

 been rather thick; fragments of it indicate that it was built up of a 

 thin outer layer and several inner layers or lamellae. A ventral valve 



