MIOCENE ECHINODEEMATA. 183 



Related forms . — S. arnoldi resembles Sismondia (?) coalingaensis and Scutella (?) merriami, 

 but differs from both in having petals extending to the margin, with straight, diverging porifer- 

 ous zones. 



Locality. — Four miles southeast of northwest end of Kettleman Hills, Coalinga district, 

 California. 



Geologic horizon. — Etchegoin formation, upper Miocene and lower Pliocene ( ?) . 



Collection.— U. S. National Museum (165538). 



Sismondia(?) coalingaensis Twitchell, n. sp. 

 Plate LXXXV, figures 2a-c. 



Description and determinative characters. — The test of this species is very small, rarely ex- 

 ceeding one-half inch in length. In marginal outline it is suboval to subovate, broader posteri- 

 orly than anteriorly. The whole form much depressed, slightly tumid centrally; margin rather 

 thin. Apex subcentral or slightly excentric posteriorly. Lower surface concave. 



The ambulacral petals are subelliptical in outline, extending a little more than halfway to 

 the margin; the posterior pair shorter than the anterior pair; pores round, pairs of pores con- 

 jugated. The whole test is covered with small but conspicuous tubercles, scattered irregularly. 



The apical system is subcentral or slightly excentric posteriorly, coincident with the apex. 

 The details could not be made out on the specimen studied. 



The peristome and ambulacral grooves could not be made out. The periproct is small, 

 inframarginal, almost marginal. 



Dimensions. — Length 12 miihmeters; width 10 millimeters; height-2 millimeters. 



Related forms. — S. coalingaensis resembles Sismondia ( ?) arnoldi and Scutella ( ?) merriami. 

 From the former it differs in having shorter, subelliptical petals and from the latter in lacking 

 the tumid petals and in having a more longitudinally oval marginal outline. 



Locality. — Jacalitos Creek, half a mile east of Kreyenhagen's, Coalinga district, California. 



Geologic horizon. — Etchegoin formation, upper Miocene and lower Pliocene (?). 



Collection. — U. S. National Museum (165717) . 



Family SCUTELLIDiE. 



Genua SCtTTELIiA Lamarck. 



Scutella andersoni Twitchell, n. sp. 



Plate LXXXV, figures 3a-d. 



Scutella sp. A., F. M. Anderson 1905, California Acad. Sci. Proc, 3d ser., Geology, vol. 2, No. 2, p. 193, PI. XIII. fig. 8. 



Determinative characters. — Test small; suboval to broadly subovate, broadest posteriorly; 

 margin thin, more so posteriorly than anteriorly, with rather pronounced notches opposite the 

 posterior petals; the whole form greatly depressed, the upper surface ridged along the longitu- 

 dinal median line, sloping rather steeply away from the ridge to the side edges; apex excentric 

 anteriorly; under surface slightly concave longitudinally. Apical system decidedly excentric 

 anteriorly, about coincident with the apex. Posterior ambulacral petals slightly longer than the 

 anterior paired petals which are slightly longer than the odd petal. Peristome excentric anteri- 

 orly. Periproct very small, supramarginal. 



Dimensions. — Length 25 millimeters; width 25 millimeters; height 5 milhmeters. 



Description. — This interesting species was briefly described and figured in 1905 by F. M. 

 Anderson but was not given a specific name. It is here named in honor of Mr. Anderson. The 

 test is small, ranging from less than a half to slightly more than an inch in diameter. In mar- 

 ginal outline it is suboval to broadly subovate; broadest posteriorly, usually about as long as 

 wide. The margin is thin, more so posteriorly than anteriorly, with rather pronounced notches 

 opposite the posterior petals and sometimes with faintly defined notches opposite the anterior 

 paired petals. The whole form is greatly depressed; the upper surface having a more or less 

 well defined ridge extending along the longitudinal median line and involving the odd petal, 



