PALEONTOLOGY. 493 



form in direction as seen in the coral, but are vertical, lateral or oblique in 

 direction indiscriminately; but are confined principally to the lower side 

 and margins of the mass ; which is about seven by four and a half inches 

 in diameter and nearly three inches thick, of an elongated oval and sub- 

 hemispherical form. 



Although the shells have much the form of Modiolopsis in general 

 outline, and have large anterior and posterior muscular scars, with an 

 entire pallial line, they differ much in surface characters, being strongly 

 marked by regular, elevated, concentric ridges, parallel to the margin of 

 the valves. This structure is so markedly different from that of Modio- 

 lopsis, that, when taken in connection with the burrowing habit, I think 

 it necessary to place them under a distinct generic head, and therefore 

 propose for them the name Corallidovnis; in allusion to their habitat, and 

 designate them as Corallidomus concentricus, from the concentric surface 

 markings, with the following diagnosis of generic and specific characters. 



Genus CORALLIDOMUS, New Genus. 

 Korallion, a Coral and Domos, a House. 

 A bivalve mollusk having anterior and posterior muscular scars, and 

 an integral pallial line ; shell oblong, with an external ligament and some- 

 what modioliform outline, coupled with a burrowing habit of life. Type 

 C. concentricus. 



Corallidomus conce?itricus, New sp. 

 Plate XIII. 



Fig. 2. 



Fig. 1.* View enlarged of a shell restored, the measurements taken from the two 



best specimens. 

 Fig. 2. Enlarged view, two diameters, of the right side of the shell indicated by 



the cross on the large figure. The shell is exfoliated and reveals the muscular 



markings. 



Shell small, twice as long as high, and moderately ventricose; cardinal and 

 basal margins subparallel, generally converging slightly anteriorly; valves subangu. 

 jar along the umbonal ridge; beaks small, rather pointed anteriorly, situated atabout 

 one-fourth of the entire length of the shell from the anterior end ; anterior end rounded 

 below the median line of the valve, posterior end obliquely truncated and broad ; sur_ 

 face of valves marked by even, sharply elevated, concentric ridges or lamellae, which 

 are abruptly curved in crossing the umbonal ridge, presenting or rather accentu- 

 ating the slight angularity of the ridge. 



Formation and Locality. — In the Cincinnati Shales of the Hudson 

 River group, Brown County, found in its native burrows in Labechia 

 Ohioe?isis Nich. 



I regret that the cut for figure 1 has been lost since it came into my possession. F. O. 



