MARYLAND GEOLOGICAL SURVEY 499 



Family ACTINOPTYCHE/E. 



Genus ACTINOPTYCHUS Ehrenberg. 

 ACTINOPTYCHUS HELIOPELTA Grimow. 



Plate CXXXIV, Fig. 3. 



Actinoptychus heliopelta Grunow. 



Seliopelta Metii Ehrenberg, 1844, Monatsb. d. k. Akad. d. Wiss., Berlin, p. 268. 



Heliopelta Leetiwenhockii Ehrenberg, 1844, Monatsb. d. k. Akad. d. Wiss., Berlin, 



p. 268. 

 Heliopelta Euleri Ehrenberg, 1844, Monatsb. d. k. Akad. d. Wiss, Berlin, p. 268. 

 Heliopelta Leeuwenhockii Ehrenberg, 1856, Mikrogeologie, pi. 33, xviii, fig. 5. 

 Heliopelta euleri Ehrenberg, 1856, Mikrogeologie, pi. 33, xviii, fig. 6. 

 Actinoptychus heliopelta Schmidt, 1875, Atlas der Diatomaceen-kiinde, pi. cix, fig. 2. 

 Actinoptychus heliopelta Van Heurck, 1881, Syu. Diat. Belg., pi. cxxiii, fig. 3. 



Description. — Valve circular, divided into sectors, from six to twenty, 

 alternately elevated and depressed. Central space stellate, hyaline. 

 Border with numerous spine-like processes. Surface reticulate and 

 granular. Diam. .297 mm. (av.). 



This is the most elegant of all the American diatoms. Its presence in 

 an undisturbed deposit is an undoubted indication of the lower horizon 

 in which it is found. 



The specific names quoted above, with numerous others, distinguished 

 forms which differed from each other chiefly in the number of sectors or 

 divisions of the valve. 



Occurrence. — Calvert Formation. 1 mile east of Marriott Hill, 

 1 mile south of Chesapeake E. E. Bridge, 1 mile northwest of West Eiver, 

 1 mile north of Jewell, 1 mile north of Jones Point. 



Collection. — Maryland Geological Survey. 



Actinoptychus praetor Schmidt. 



Actinoptychus splendens Shadbolt. 



Actinoptychus undulatus Kiitzing. 



Plate CXXXIV, Fig. 4. 



Actinocyclus sp. Bailey, 1842, Amer. Jour. Sci., vol. xlii, p. 105, pi. ii, figs, ft, 10, 11. 



Actinocyclus imdulatus Kiitzing, 1844, Bacill., p. 132, fig. xxiv. 



Actinoptychus undulatus Kali's, 1861, in Pritchard's Infusoria, p. 839, pi. v, fig. 88. 



Description. — Valve circular, divided into six sectors, alternately ele- 

 vated and depressed. Surface cellular and punctate. Processes three. 



