DESCRIPTION OF SPECIES 201 



dividuals from the Harrison ore and the Lower Mercer limestone. The 

 single specimen obtained from the Harrison ore occurs in the form of 

 an internal cast, which, however, is sufficiently well preserved to be 

 referred with considerable confidence to N. beyrichi. 



Horizon and locality. Harrison ore: Jackson County, Locality 1, 

 r. Lower Mercer limestone: Licking County, Locality 46, r. 



Nucula elongata n. sp. 

 PL X, figs. 10-13 



Description. Shell small, subtriangular, much produced ante- 

 riorly, length almost twice the height, greatest width slightly below the 

 middle of the shell, gibbous in posterior portion, the greatest convexity 

 occurring midway between the beaks and the ventral margin, shell 

 flattened anteriorly. Umbonal region prominent, beak small, elevated 

 and incurved over the hinge line, directed posteriorly, situated about 

 one-fourth the length of the shell from the posterior margin; cardinal 

 margin sloping from the beak to the extended anterior extremity; 

 posterior extremity regularly rounded forming a continuous curve with 

 the rounded ventral margin which anteriorly extends slightly upward; 

 anterior extremity produced and pointed. Surface of internal mold 

 smooth except for a few faint lines of growth; occasionally indications 

 of fine concentric lines. 



Dimension's. Considerable variation exists in the size of the in- 

 dividuals as may be seen by the following measurements, the first of 

 which is the holotype: 



Maximum length llmm. 9mm. 7mm. 6mm. 



Height from beak to opposite margin 6.2 mm. 5.5 mm. 4.5 mm. 3.5 mm. 

 Thickness of single valve 2mm. 1.5mm. 1.2mm. 1mm. 



Remarks. This species is common in the Sharon ore at a single 

 locality in Scioto County where it occurs in an excellent state of preser- 

 vation in the form of internal casts. It is closely related to N. parva 

 McChesney and to N. beyrichi von Schauroth, but can be easily dis- 

 tinguished from either species by its much more produced anterior 

 end. It is associated with two other species, common in the Sharon 

 ore N. subrotundata Girty mss. and N. lunulata Girty mss. A single, 

 somewhat imperfect individual from the Lower Mercer limestone at 

 Bald Knob, also in the form of an internal cast, agrees closely with 

 the species as it occurs in the Sharon ore, although its otherwise appar- 

 ent total absence from any horizon above the Sharon tends to throw 

 much doubt upon the identification. 



Horizon and locality. Sharon ore: Scioto county, Locality 2, c. 

 Lower Mercer limestone: Licking County, Locality 46, r. 



