Makylaxd Geological Survey 359 



species and is llie only one which the writer has seen from the Lower 

 Devonian of the State. 



Occurrence. — Helderberg Formation, Keyser Member. Pinto. 



Collection. — U. S. National Museum. 



MOLLUSCOIDEA 



Class BRYOZOA 



Order CTENOSTOMATA 



Family RHOPALONARllDAE 



Genus RHOPALONARIA Ulrich 



Ehopaloxaria attenuaia Ulrich and Bassler 



Plate XLYI, Kg. 1 



Rhopalonaria attenuata Ulrich and Bassler, 1904, Smith. Misc. Coll., vol. 

 xlv, p. 268, pi. Ixvi, figs. 4, 5. 



Description. — Several imperfectly preserved specimens from the Keyser 

 limestone at Cash Valley agree very well with this widely distributed 

 Silurian species, although it is possible that better specimens might show 

 more relationship to the Devonian species of the genus. The various 

 forms of Rhopalonaria are exceedingly alike and in the absence of good 

 specimens, close specific determination is almost impossible. It must also 

 be remembered that in this genus practically all the species are repre- 

 sented only by the clay filled or empty excavations left by the parasitic 

 zoarium which excavated the surface of its host. 



The zoarium of Rhopalonaria attenuata is adnate, and is usually about 

 half embedded in its host which most often is a coral, crinoid stem, or 

 brachiopod. The zoa?cia are unknown, in fact the excavations undoubtedly 

 represent only the creeping basal portion of the zoarium. As will be noted 

 from fig. 1 on pi. xlvi, this basal portion consists of well-defined fusiform 

 internodes or colls connected by delicate stolons, all being arranged in a 

 pinnate manner. The extreme tenuity of its parts and the rigidity of their 

 arrangement are particularly characteristic of the present species. 



Occurrence. — Helderberg Formation, Keyser Member. Cash 

 Valley. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



