610 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxv. 



is fully as prominent as that of the ventral valve. It curves forward 

 at the center and extends well out on the cardinal slopes. The flexure 

 lines are clearly defined well out toward the lateral margin. The striae 

 of growth cross the area parallel to the base. 



The cast of the interior of the ventral valve shows only the outline 

 of the visceral cavity and that the main vascular sinuses extend a con- 

 siderable distance in advance of the visceral cavity. The cast of the 

 interior of the dorsal valve shows that it had a strong, broad, central 

 ridge divided by a faint longitudinal median sinus. Only traces have 

 been seen of the main vascular sinuses. 



Ohservations. — This is a very pretty little species that I confused 

 with the young of OhAim {Linguleph) gregtoa in the absence of well- 

 defined specimens. Material collected by Mr. S. Ward Loper at the 

 type locality proves that the shell difl'ers considerably from the young 

 of O. (Z.) gregwa. It also difl'ers, in being regularl}^ oval, from 0. 

 (Z.) colllcia Matthew, with which it is associated, and (>. (Z.) canivs 

 Walcott, from the Pamdoxldes horizon of Cape Breton. 



Formation and locality. — Middle Cambrian, Matthew's Etchemin- 

 ian, just above the conglomerate at the base of the section on Dougal 

 Brook, branch of Indian River, Cape Breton, Nova Scotia. 



OBOLUS (LINGULELLA) COLLICIA Matthew. 



Leptoholusf collicia Matthew, Bull. Nat. Hist. Soc. New Brunswick, IV, 1899, 

 p. 200, pi. I, figs. 3 a-c. 



This shell is associated with 0. (Z.) atanus. It ditfei's from it in 

 being larger and in having a more acuminate and ])roader ventral valve 

 and a more broadly oval dorsal valve. The exterior surface is marked 

 by very fine, slightly irregular, concentric stria?. 



Formation and locality. — Middle Cambrian, Matthew's Etchemin- 

 ian, just above the conglomerate at the base of the section on Dougal 

 Brook, branch of Indian River, (^ape Breton, Nova Scotia. 



OBOLUS (LINGULELLA) CANIUS, new species. 



Shell small ; general form elongate oval, with the ventral valve 

 slightly acuminate. In both the ventral and dorsal valve the shell 

 narrows posteriorly, the front being broadly rounded. The convexity 

 of the two valves is well marked, and it is nearly the same in each. 



Surface of the shell marked by fine concentric stria? and a few lines 

 of growth. When the outer shell is exfoliated fine radiating stria? 

 cross the fine concentric strife. The shell appears to be of moderate 

 thickness and formed of several thin layers or lamellas. The largest 

 ventral valve in the collection has a length of 5 mm. and a width of 3 i 

 mm., and a dorsal valve 4 mm. in length has a width of 2 mm. 



The area of the ventral valve is elongate, being nearly one-fifth 

 the length of the shell. It is divided midway by a very distinctly 



