282 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvm. 



opposite the head of the delthyrium to a plate two-thirds or more of 

 the length of the delthyrium. 



Dorsal valve uniformly and moderately convex, with the apex 

 curved over to the edge of the low area; area divided by a broad 

 delthyrium; casts of the interior show that the crura were strong, 

 dental sockets shallow, and that the crural plates extended across 

 the umbonal cavity, uniting to define what may be called a pseudo- 

 curalium. No trace of a cardinal process has been seen in a large 

 number of casts of the interior, and Messrs Hall and Clarke did not 

 find any in a large amount of material. 



The casts of the interior show that the sliell was minutely punctate, 

 and a shell preserving some of the inner layers has every appearance 

 of punctate structure, 



Ohservations. — This species ditfprs from all recognized species of 

 the genus by its surface ribs and stria?. 



For) nation and locality. — Middle Cambrian. Paradoxides zone. 

 Dark argillaceous shales of division Ic, Seeley street, St. John, Port- 

 land Brook and Ratclifl's Millstream, New Brunswick. 



PROTORTHIS HELENA, new species. 



This species is founded on the cast of a ventral valve associated with 

 Protosijyhon kenvpanimi. The form of the spondylium and area is 

 like that of Protorthis latourensif<.^ but the smooth shell with a broad, 

 rounded mesial sinus is unlike that species and also other species 

 of the genus. The shell appears to have been thicker than that of 

 P. latoiirensl.^. Only traces of growth lines are preserved on the cast. 

 The ventral valve is 10 mm. long with a width of 14 mm. The cast 

 shows that the teeth and dental plates were unusually strong. 



This species difi'ers from all others of the genus by its smooth or 

 nearly smooth surface and strong median sinus. It suggests Syntro- 

 phia hiTobuensm at first sight, but there is no evidence of a median 

 septum supporting the spond^dium. 



The specific name is that of Mrs. Walcott who collected the specimen. 



Formation and locality. — Middle Cambrian, St. John formation, 

 Kennebecasis River, St. John County, New Brunswick. 



PROTORTHIS LATOURENSIS Matthew. 



Kuionfma kitoureiisis Matthew, Trans. Roy. Snc. Canada, III, 1886, p. 42, pi. v. 



figs. 18, 18a-c. 

 Kuiorglna latoarensis Hall and Clarke, Pal. N. Y., VIII, 1892, Pt. 1, pp. 93, 95, 

 238, pi. IV, figs. 18, 19, 20. 

 Original description. — ^Valves narrowly semicircular, broader than long, flat; umbones 

 low; greatest thickness in the posterior third; hinge line shorter than the width of 

 the shell. 



Dorsal valve with a distinct median der)ression extending from the umbo to the 

 front margin, and with low ridges diverging from the Ijeak toward the lateral third 

 of the front of the valve. (Jmbo not elevated above the hinge area, which is exceed- 



