Maryland Geological Survey 483 



lateral contact near the anterior extremity, coiled in such a plane that the 

 upper of the tubes is in contact at the aperture with the lower of he pre- 

 ceding volution; external surface smooth; cross-section of apertures cir- 

 cular. 



The species is doubtless similar in composition to the form described 

 by Conrad under the name of Diploconcha. The fusing of the constituent 

 tubes along the contacts is a common phenomenon in the recent grega- 

 rious Vermetidce and is a character of no systematic value whatever. 



The species suggests S. rotula Weller, but is larger and less regularly 

 coiled. 



Occurrence. — Monmouth Formation. Brightseat, Prince George's 

 County. 



Collection. — Maryland Geological Survey. 



Genus VERMETUS Adanson 

 [Hist. Nat. Senegal, 1757, p. 160] 

 Type. — Vermetus adansoni Daudin. 



.Shell usually fixed, rarely free ; regularly coiled in the young of some 

 species, loosely and irregularly twisted in the adults of all ; internal septa? 

 usually present ; aperture circular ; majority of species operculate. 



Vermetus circularis (Weller) 



Serpula circularis "Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 

 p. 307, pi. xix, figs. 5, 6. 



Description. — " Tube rather large, moderately thick, increasing gradu- 

 ally in size, the increase being more rapid as it approaches the aperture, 

 not closely coiled, the first volution of the type specimen forming a rather 

 large irregular circle, after which the shell is in contact for about one- 

 fourth volution nearly to the aperture. Another specimen is perhaps not 

 in contact at all. Aperture more or less subcircular or subelliptical in 

 outline. The surface of the shell is marked by more or less irregular, 

 annular lines of growth. The dimensions of the type species are: 

 Greatest diameter of aperture, 8 mm. ; length of tube, 72 mm. ; greatest 

 diameter of space within first volution, 13 mm." — Weller, 1907. 



Etymology: Vermis, a worm. 



