SIPHONOTRETID^. 623 



SCHIZAMBON MANITOUBNSIS n. Sp. 

 Plate LXXXIV, figures 3, 3a-e. 



General form and convexity much like those of ScMsamhon typicalis Walcott, also surface 

 characters if the influence of the different matrix is allowed for. The differences between the 

 two species are in the larger foramen in S. manitouensis; in a shorter depression before the beak; 

 in the interior markings of the dorsal valve and the strong area of the dorsal valve (PI. LXXXIV, 

 fig. 3c). There may be a similar area in ;S^. typicalis, but owing to the condition of preservation 

 it has not been observed. 



The finely spinose surface is rarely seen, as it adheres to the matrix. The usual appearance 

 of the shell is like that shown by figure 3. The average shell has a length of 4.5 mm., width 

 about the same. Substance corneous. 



The specific name is derived fi'om Manitou, Colorado. 



Formation and locality. — Lower Ordovician: (186 and 186a) « Near line of contact between the red and gray 

 Ordovician limestone, in siliceous red limestone about 30 feet {9.1 m.) above the pre-Cambrian rocks, Williams Canyon, 

 Manitou; and (360) red siliceous limestone near Colorado Springs; both in El Paso County, Colorado. 



ScHizAMBON PRiscus Matthew. 

 ''■ Plate LXXXIV, figures 2, 2a-e. 



Schizambon priscus Matthew, 1901, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 4, No. 19, pp. 277-278, PL V, 

 figs. 4a-d. (Described and discussed as a new species. None of the specimens figured are reproduced in this 

 monograph.) 



Schizambon priscus Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, pp. 187-189, PI. XI, 

 figs. 6a-d. , (Description and figures copied from preceding reference.) 



Shell small and subcircular to transversely ovate, moderately convex. Ventral valve 

 slightly acuminate, with the apex above a short false area, and lower than the umbo. Foramen 

 small, oval, and opening externally into an elongate groove tapering toward the beak; back of 

 the foraminal opening a tapering ridge extends to the beak, leaving a narrower groove on each 

 side. In the interior of the shell the edges of the tapering groove are slightly elevated and the 

 foraminal opening appears to be of about the same size as the external opening. On some 

 specimens of the ventral valve, on each side of the foramen on the outer surface, a narrow depres- 

 sion extends forward and slightly outward nearly to the front margin ; this character corresponds 

 to the low ridges in the ventral valve of Schizambon typicalis Walcott (PI. LXXXIV, fig. la). 



The dorsal valve is less convex than the ventral, and its beak is marginal. The interior 

 of the valve shows a median ridge of varying strength, and the same is true of the ridges indi- 

 cating the narrow main vascular canals. In figure 2c the anterior portion of the median 

 ridge is shown, also the oval, widely separated central muscle scars (h) and the small anterior 

 lateral scars (j); in figure 2d the main vascular canals and the central portion of the median 

 sinuses are shown. In figure 2e there is only a trace of vascular markings. 



Surface as preserved, marked by very fine radiating and concentric ridges that form on some 

 shells a cancellated pattern; the fact that many shells adhere by the outer surface to the matrix 

 leads me to suspect that the outer surface is roughened and probably spinose as in other species 

 of the genus. The average size of the shells is about 4 mm. in length and width. Shell substance 

 corneous. 



Formation and locality. — tTpper Cambrian: (lOf and lOg) Shales on the east branch of Barachois River, 0.75 

 mile (1.2 km.) north of the crossroad from Boisdale to Upper Leitches Creek; (lOh) at same locality as Locality lOf, 

 but in shales of a slightly different horizon; (lOe) shales on the east branch of Barachois River, 0.5 mile (0.8 km.) 

 north of the crossroad fi-om Boisdale to LTpper Leitches Creek; (101) shale on east bank of Barachois River, 6 miles 

 (9.6 km.) from Little Bras d'Or Lake; (13h) shale on the east bank of Barachois River, 1.5 miles (2.4 km.) north of 

 Boisdale; (10k) shale on west bank of Barachois River, about 0.25 mile (0.4 km.) north of the Boisdale road; (lOd) 

 shale on the west side of Barachois River, 0.125 mile (0.2 km.) north of the Boisdale road, opposite McMullin's place; 

 (lOi) shale in high bank on the west side of Barachois River, just north of the Boisdale road; (307 [Matthew, 1903, p. 

 1S8]) shales of Division C3c of Matthew on McLeod Brooh (=Barachois River); (3q) shale in Barachois Glen, 4 miles 



a 186a is the type locality. 



