CRETACEOUS ECHINODERMATA. 49 



Localities. — Upper part of the bluff of Red River, Larnar County, and 10 miles above the 

 mouth of Kiamesha Creek (type); 3 miles west of Denison (figured specimen); railroad cut 

 west of Austin; and "Gap," Travis County, Tex. 



Geologic horizon. — Denison formation of Washita group, Comanche series, Cretaceous. 



Collection.— \] . S. National Museum (2176S). 



Subclass REGULARIA ECTOBRANCHIATA. 



Order DIADEMOIDEA. 



Suborder CALYCINA. 



Family SALENIID^I. 



Genus SALENIA Gray. 



Salenia texana Credner. 



Plate XII, figures la-i; Plate XIV, figures la-c. 



Cidaris diatretum Giebel, 1853, Naturwiss. Ver. in Halle Jahresb. for 1852, p. 374, PI. VII, figure 2. 

 Salenia texana Credner, 1875, Zeitsclir. fur gesam. Naturwiss., vol. 46, pp. 105-116, PI. V, figs. 1-6. 

 Salenia texana Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 75. 

 Salenia texana Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Salenia texana Clark, 1S93, U. S. Geol. Survey Bull. 97, pp. 40, 41, PI. X, figs. la-h. 

 Salenia texana Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., pp. 163, 164. 



Determinative characters. — Test subglobose; upper surface convex; sides inflated; under 

 surface flat. Ambulacra narrow, flexuous, with two rows of mammiUated granules in each area ; 

 poriferous zones flexed; pores uniserial. Interambulacra wide, with two rows of alternating 

 plates, six in each row. Apical system large, convex, subcircular; periproct prominent. Peri- 

 stome moderately large. 



Dimensions. — Diameter 10 to 2.5 millimeters; height 7 to 20 millimeters. 



Description. — Credner presents the first complete diagnosis of a North American Mesozoic 

 echinoid in the detailed descriptions accorded the present species. Its reference by Giebel in 

 1852 to Cidaris diatretum ( = Pseudodiadema diatretum) was erroneous. 



The test is subspherical when complete, but in many of the specimens examined is somewhat 

 flattened, both actinally and abactinally. The lower surface is slightly concave in the vicinity 

 of the peristome. The sides are inflated, presenting a rounded surface which is fuller above 

 than below. 



The ambulacra are narrow, increasing gradually in width from the apical system to the 

 peristome. Two rows of mammillated granules, twenty-four to twenty-six in each, occupy the 

 middle of each area. Very minute granules extend in a fine between the rows and in the vicinity 

 of the peristome surround the larger granules themselves. The poriferous zones are narrow and 

 flexuous, and the pores are regularly arranged in a uniserial series; near the peristome they are 

 slightly more crowded. The most pronounced flexure is opposite the second interambulacral 

 plate from the apical system. Toward the peristome the zones become nearly straight. 



The interambulacra are broad and formed of two alternating rosvs of broad plates, six in 

 each row. The tubercles increase rapidly in size from the peristome, where they are scarcely 

 larger than the mammillated granules of the ambulacra. The areolas are large and surrounded 

 by mammillated granules of various sizes that are crowded together along the inner edge of the 

 plates. Between the larger granules are numerous minute granules. The areola rises to a prom- 

 inent boss that is deeply crenulated and bears an imperforate mamelon. 



The apical system is very large, convex, subcircular, with radiating ridges that extend from 

 the ovarial openings of each plate and unite with similar ridges of adjacent plates. Small punc- 

 tures are found at the angles of the plates and intermediate between them. The subanal plate 



