MARYLAND GEOLOGICAL SURVEY 749 



sculptured and bearing the same relation to the enclosing tube made the 

 theory of chance association untenable. Nothing like these forms has been 

 observed in any branch of the animal kingdom, but they are less unlike 

 the worms than any other phylum. There is, too, a wider range of 

 variation in the Yermes than in any other of the major divisions. There 

 are groups in which a calcareous operculum is secreted and groups in 

 which the tube is gradually constricted toward the aperture and, although 

 the combination of these two rather unusual characters is not known, yet 

 it is not without the range of possibility. The sculpture, however, is much 

 more regular and elaborate than any observed on the opercula of recent 

 worms. 



Professor Grabau, of Columbia University, to whom squeezes of the 

 ornamented ends were shown, suggested that they might be the impres- 

 sions of a test of a degenerate gastropod, possibly allied to the Acmaeas, a 

 hypothetical genus, which, when it lost the power to coil through lack of 

 vitality, continued to grow in a plane at a high angle to that of the shell. 

 So little is known of degenerate gastropods that one cannot define their 

 limits of variation, and there is a possibility that this may be a bizarre 

 type which arose, together with many other degenerate mollusca near the 

 close of a great era. The writer is also under obligations to Mr. J. E. 

 Benedict and Mr. Austin H. Clark for their suggestive interest in these 

 organisms. 



Occurrence. MONMOUTH FORMATION. Brooks estate near Seat Pleas- 

 ant, Prince George's County. 



Collection. Maryland Geological Survey. 



ECHINODERMATA 



CLASS ECHINOIDEA 



Order CIDAROIDA 



Family CIDARIDAE 



Genus CIDARIS Leske 

 ClDARIS Sp. 



Description. Several fragmentary spines belonging to this genus were' 

 found amongst other materials from Appoquinimink Creek, Delaware. 

 Two of the specimens show the basal portions of the spine with the collar 



