North American index fossils, invertebrates . Fig. ^936. Linthia variabilis, several plates of the left posterior petal, greatlyenlarged ; apical system, greatly enlarged; several plates of the anterior petal, greatlyenlarged. (After A. W. Slocum.) strongly elevated and truncate; ambulacral petals proportionatelyshorter and broader. Ripleyan of L. tumidula Clark. (Fig. 1937, a-J.) Cretacic. Test elevated. Apex central. Posterior border obliquely trun-cated, bearing the anal opening. Fascioles distinct. Jerseyan (Vincentown lime sand) of New Jersey. 6o2 NORTH AMERICAN INDEX FOSS
North American index fossils, invertebrates . Fig. ^936. Linthia variabilis, several plates of the left posterior petal, greatlyenlarged ; apical system, greatly enlarged; several plates of the anterior petal, greatlyenlarged. (After A. W. Slocum.) strongly elevated and truncate; ambulacral petals proportionatelyshorter and broader. Ripleyan of L. tumidula Clark. (Fig. 1937, a-J.) Cretacic. Test elevated. Apex central. Posterior border obliquely trun-cated, bearing the anal opening. Fascioles distinct. Jerseyan (Vincentown lime sand) of New Jersey. 6o2 NORTH AMERICAN INDEX Fig. 1937- «-^, Linthia tumidula, upper, lateral, lower and posterior views, X Vz >e,fy Echinocardium orthonotum, lower and lateral views, X M* (After Clark.) XXXIIL Maretia , subpentahedral echinoids with more or less flattenedtest; petaloid ambulacra long and rather narrow, in shallow grooves,the anterior one reduced and nearly flush; peristome small, excen-tric on flat under side; periproct on swollen posterior end, abovethe margin. Interambulacra with comparatively coarse tubercles,except the posterior one; on the actinal side the posterior ambu-lacral spaces are smooth. Eocenic-Recent. 51. M. ruspatangus Conrad. Oligocenic. Anterior end with faint impression by frontal groove, dyingaway upwards; form slightly heart-shaped; posterior ambulacrumslightly keeled, highest point of shell being formed by it. Differsfrom recent M. planiilata in its more truncated anterior and lesspointed posterior end and much greater height. Length of averagetest, 65 mm.; greatest width
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