MARYLAND GEOLOGICAL SURVEY 455 



Genus RHOPALODICTYUM Ehrenberg. 



Rhopalodictyum marylandicum n. sp. 

 Plate CXXX, Fig. 14. 



Descnption. — Arms club-shaped, of different sizes, and at unequal 

 distances; lengths of arms in proportion of 23:33:26; angles of arms 

 = 100°, 130°, 130°; the longest arm opposite one of the larger angles; 

 arms 2 times as long as the breadth at the end, breadth at the end 2^ 

 times the breadth in the narrowest part; central disk f as wide as the 

 end of an arm; two concentric rings in the central disk. 



Occurrence. — Calvert Formation. Popes Creek, Lyons Creek. 



Collections.— Maryland Geological Survey, Johns Hopkins University, 

 Rev. Edward Huber. 



Rhopalodictyum calvertense n. sp. 

 Plate CXXX,- Fig. 15. 



Description.— Arms short, club-shaped, with large subspherical ends, 

 greatest width of the arms seven-eighths the length, least width one- 

 fourth the length; lengths of arms in the proportions 18 : 19 : 20 ; angles 

 of the arms = 129°, 119° and 112° ; greatest angle opposite the shortest, 

 least angle opposite the longest, and medium angle opposite the medium 

 arm; central disk with three concentric rings. 



Occurrence.— Calxei^t Formation. Lyons Creek. 



Collections.— Maryland Geological Survey, Johns Hopkins University, 

 Rev. Edward Huber. 



Family PORODISCIDA. 



Genus PORODISCUS Haeckel. 



PoRODiscus concentricus (Ehrenberg). 



Plate CXXX, Fig. 16. 



Flustrella concentrica Ehrenberg, 1838, Abhand. d. k. Akad. d. Wiss. Berlin, p. 132. 

 ? FluMrella concentrica Ehrenberg, 1854, Mikrogeologie, pi. xix, tig. 61 ; pi. xx, fig. 



42; pi. xxi, tig. 51; pi. xxxvi, tig. 29. 

 Trematodiscus concentricus Yi.&ec'ke.X, 1862, Mon. d. Radiol., p. 493. 

 Flustrella concentrica Ehrenberg, 1875, Abhand. d. k. Akad. d. Wiss. Berlin, p. 72, 



Taf. xxii, fig. 13. 

 Trematodiscus concentricus Stohr, 1880, Paleontographica vol. xxvi, p. 108. 

 Porodiscas concentricus Haeckel, 1887, Chal. Kept., vol. xviii, pt. i, p. 492. 



