492 GEOLOGY OF OHIO. 



some foreign body, and has I presume during life been attached to 

 marine plants, from which it has fallen as they were decomposed, and 

 thus been amassed on the muddy bottom. 



ANNELIDA. 



Spirorbis anthracosia. 



PLATE XII, figs. 18 and 19. 



Spirorbis anthracosia Whitf., Am. Jour. Sci., Feb., 1881. 



Shell minute, planorbiform, composed of from one to two and a half volutions, 

 tube slender, and very gradually increasing in diameter, marked by very fine, irreg- 

 ular encircling stride, which are often gathered into little knots or points near the 

 border of the open umbilicus. Lower side of the shell more or less flattened as if 

 for the attachment to some foreign substance. Diameter seldom exceeding one 

 line, generally less. 



Formation and Locality. — In the higher strata of the Coal Measures, 

 near Marietta, Ohio. 



NEW GENUS AND SPECIES OF BURROWING FOSSIL BIVALVE 



SHELL. 



Several years ago Prof. Edward Orton of the Ohio Geological Survey, 

 called my attention to a mass of Tetradium from the Hudson river group 

 Brown County, Ohio, which w y as filled with perforations or burrows 

 like those often seen in living corals, made and occupied by species of Lith- 

 odomus. On close examination several of the burrows were seen to have 

 shells, occupying them, which at the time were thought to be examples 

 of Sedgewickia ? divaricata, described in Vol. II, Pal. Ohio, p. 89, Plate 

 2, fig. 3. More recently, on closer examination, and by removing one of 

 the shells from the burrow, it proves to be a very distinct species and to 

 present some of the general appearance of a Modiolopsis. 



That the shells now occupying the burrows in this coral were the 

 original excavators of the perforations, there can be no question, I think; 

 as there are remains of no less than twelve individuals to be seen in the 

 burrows, all of the one form, while no other shell is present. Moreover, 

 they are each suited in size to the burrows they occup}\ So far as I am 

 aware no shell resembling Modiolot>sis and possessing burrowing habits, is 

 known to occur in Silurian or Devonian rocks; these therefore present 

 a new feature in the molluscan life of this period that is highly interest- 

 ing. 



The perforations or burrows in this coral are of various sizes from 

 very small ones to those more than an inch in length as seen in section 

 and of a diameter of more than a fourth of an inch, and where shells are 

 seen in them they appear of a size suited to the burrow they occupy. 

 The shells when fully grown, or what appear to be adult, are nearly or 

 quite three-fourths of an inch in length, and of nearly three-eighths of an 

 inch in height from base to cardinal margin. The burrows are not uni" 



