SYNTROPHIID^. 



809 



A group of young shells from Honey Creek shows only the smooth, slightly convex forms, 

 with only slight ventral sinus and dorsal fold. One larger shell associated with the young 

 shells has a relatively deep sinus and a trace of a plication. 



Formation and locality.— Upper Cambrian: (69) Limestone near Honey Creek; and (71) limestone in Cold 

 Creek Canyon; both in Burnet County, Texas. 



u 



HUENELLA VEEMONTANA n. Sp. 



Text figure 76. 



It is somewhat 



This species is represented by a single- specimen of the two valves united 

 imperfect near the beaks. 



Valves moderately and about equally convex, with 

 the dorsal valve subcircular in outline and the ventral 

 more elongated at the beak. Hinge short; cardinal 

 angles rounded. 



Surface marked by low, concentric ridges of growth 

 and numerous fine, rounded, radiating ridges that in- 

 crease in number from the umbo to the margin by 

 both bifurcation and interpolation of new ridges. A 

 low, moderately broad sinus occurs on the anterior half 

 of the ventral valve and a narrow median fold on the 

 dorsal valve. Wliere the surface of the shell is exfo- 

 liated the shell appears to be minutely punctate. 



The ventral valve has a length of 11 mm. ; width, 9 mm. 

 is 6 mm. 



Observations. — This shell differs from all known species of Huenella by its finely ribbed 

 surface. In this respect it recalls Swantonia antiquata (Billings) (PI. CIV, fig. 5). It occurs 

 in association with Paradoxides in an intraformational conglomerate. 



Formation and locality. — Middle Cambrian : (319s) "St. Albans formation," at St. Albans, Franklin County, 

 Vermont. 



Genus CLARKELLA Walcott. « 



A 



Figure 76. — Huenella vermontaTUt n. sp. A, Ventral 

 view of a specimen. A', Dorsal view of same speci- 

 men. A", Side view of the same specimen, showing 

 the two valves united. 



The specimen is from Locality 3193, near St. Al- 

 bans, Vermont (U. S. Nat. Mus. Cat. No. 58312). 



The convexity of the two valves 



Clarhella Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, pp. 110-111 



as a new genus.) i 



Clarkella Walcott, 1908, idem, vol. 53, No. 4, PI. XI, and pp. 142 and 148 



(Described and discussed as below 



(Classification of genus.) 



General form rotund, unequally biconvex. Surface smooth or marked by concentric striae 

 and lines of growth. Ventral valve convex at the umbo and with a strong, broad median 

 sinus; area low and divided by a relatively large delthyrium. Dorsal valve convex at the 

 umbo, which is extended forward into a strong, broad median fold. Cross sections of the 

 valves near the apex and beneath the umbo show a spondylium supported by four or more 

 septa that divide the umbonal cavity into five chambers. 



Thin sections of the shell of the type species show it to be fibrous and with many minute 

 pores arranged in lines radiating from the beak to the front and side margins of the valves. 



Type. — PolytcecMa? montanensis Walcott. 



This genus is known only by the type species from the Lower Ordovician of Montana. It 

 is distinguished from. PoJyiwcMa Hall and Clarke [1892c, p. 239] by an open delthyrium, smooth 

 surface, and presence of septa and spondylium in tlie dorsal valve. It differs from Syntrophia 

 and Huenella in having several septa supporting the spondylium, and also from Huenella in 

 having a smooth nonplicate surface. 



The generic name is given in recognition of the work of Prof. Jolm M. Clai'ke, of the Geo- 

 logical Survey of New York, in connection witli Prof. James Hall, on the fossil Brachiopoda. 



a Prior to the definition of the genus Clarkella the type species was placed under PolytacUa [Walcott, 1905a, p. 295]. 



