384 



Forty-second Report on the State Museum, 



stone for the purpose of obtaining specimens of a large Pentamerus* 

 of which, up to this time, there have been no exasnples in the State 

 Museum collections. These fossils occur in a magnesian lime- 

 stone in the condition of casts of the interior, the shell having 

 been dissolved and removed. The interior structure representing 

 the hinge, crura and the spoon-shaped process are often beauti- 

 fully preserved, and these parts, which are such an important 

 generic feature are very conspicuously developed in this species, 

 which can only be obtained in the condition just mentioned. 



The locality is interesting from the abundance of individuals 

 of this species. For an exposed thickness of eight or ten feet, in 

 one quarry, these fossils are so abundant that no piece of lime- 

 stone of six inches cube could be obtained without their presence, 

 and they are literally crowded together in the limestone layers. 

 The rock at this place has been quarried, and burned for lime, 

 over an area of fully half an acre. The many tons of loose rock 

 still remaining in the abandoned quarry, and the escarpment 

 still exposed, show that the entire bed has been of the same 

 character. At a point on the old Wabash canal, about a mile dis- 

 tant from the place just designated, there is an outcrop of appar- 

 ently the same layer of limestone and equally filled with these 

 Pentameri. 



The stratum (or several strata the entire thickness of which 

 remains unascertained) is nearly or quite at the upper limit of the 

 Niagara group and in this neighborhood is apparently the upper- 

 most layer. I am not aware that the species has been found in 



*This species was originally figured by Prof. E. Emmons in bis Manual of Geology 

 published in i860, under the name Pentamerus nobilis. No description or reference to 

 locality was ever published by him so far as I know. The fossil is widely distributed 

 in the public and private collections of the country. 



It is often labeled Pentamerus Kuightii and I do not recollect to have anywhere seen 

 it under the name of P. nobilis. This is undoubtedly the species described by Conrad 

 under the name Pentamerus laqueatus. Proceedings Acad. Nat. Sci. Phila. Vol. 7, p. 441, 

 as follows: " Ovate, large valve inflated with about twenty-eight angular ribs; mesial 

 ridge but little prominent, with 5-G ribs rather larger than the others. Smaller valve 

 slighrly ventricose, with a wide but shallow depression on each side; basal margin 

 sinuous. Loc. Delphi, Ind. Mrs. Hill. The species resembles the P. Aylesfordii but is 

 quite distinct." 



This description antedates the figure of Prof. Emmons by five years, and although 

 itm.-iy be regarded as meagre, the comparison with P. Aylesfordii is sufficient to dis- 

 tinguish it from auy other American species. In its form and general oharacter it 

 more nearly approaches P. Kuightii {—P. Aylesfordii) than any other American form, but 

 it is quite distinct in many important characteristics. I shall endeavor to give some 

 further information regarding its character, mode of occurrence and its relations to 

 P. Kuightii and other forms of the genus. 



