MARYLAND GEOLOGICAL SURVEY 433 



resent several other species in addition to those here described, but are 

 not sufficiently well preserved for identification. 



Class OPHIUROIDEA. 

 Order OPHIURE/E. 



Genus OPHIODERMA Muller and Troschel. 



Ophioderma ( ?) SP. 



Plate CXX, Fig. 3. 



Fragments of the arms of an Ophiurian occur in the indurated ledge 

 just above sea level along St. Mary's Eiver. It is impossible to deter- 

 mine the relations of the form with accuracy, but it is probably an 

 Ophioderma. The fragments were found in the interior of the shells of 

 large gastropods. 



Occurrence. — St. Mary's Formation. St. Mary's Eiver. 



Collection. — Maryland Geological Survey. 



COELENTERATA. 



Class HYDROZOA Huxley. 

 Order TUBULARIy^ Allman. 



Genus HYDRACTINIA v. Beneden. 



Hydractinia multispinosa ' n. sp. 



Plate CXXI, Figs. 1-9. 



Description. — Skeleton laminated, forming crusts varying in thickness 

 from 0.2 mm. to 2.5 mm. over the shells of gastropoda; invested shell 

 often wholly absorbed and replaced by the growing coral. Surface rough, 

 studded with closely and rather regularly arranged conical tubercles or 



1 Cfr. Hydractinia circumvestiens Wood, 1844, as figured and described by Nicholson, 

 18*86, Monog. Brit. Stromatoporoids, Palseontographical Society, vol. for 1885, \i. 68, 

 pi. vi, flgs. 7-13; also H. plioccena Allman, 1873, Geol. Mag., No. 98, p. 337, and 

 Carter, 1877, Ann. & Mag. Nat. Hist., vol. xix, 4th ser., p. 52, pi. viii, figs. 7-10; and 

 H. michelini Fischer, 1857, Bull. Soc. Geol. France, vol. xxiv, p. 689 (= Cellepora 

 echinata Michelin, 1847, Iconographie Zoophytologique, p. 74, pi. 15, fig. 4). 

 28 



