2ri8 



PROCEEDINGS OF THE N AVION A L MUSEUM. 



vol.. XXXII. 



of the former genus we find "beneath and on each side of the beak is 

 a concave, sharply defined space, but no proper cardinal area/' In the 

 description of Beaehia it is stated that: "The cardinal margin beneath 

 the beak is flattened into a well-defined pseudo-area/' In the speci- 

 mens before us there is a distinct flattened cardinal area the presence 

 of which is the natural consequence of the great thickening and ele- 

 vation of the beak portion of that valve. To the writer this difl'erence 

 is not of more than speciflc rank; the younger forms present only a trace 

 of the areal flattening. In the following description of the species 

 this character is therefore regarded as one of the specific marks of the 

 Maine specimens consequent upon the extreme thickening of the shell. 

 The accompanying figures represent the molds of the interior of a 

 pedicle and brachial valve of full size, as they appear in the rocks of 

 Chapman Township, Aroostook County, Maine. 



Fig. 1.— Rensselaeria mainensis, mold of 

 interior of pedicle valve. nat. size. 



Fig. 2. — Rensselaeria mainensis, mold of 



INTERIOR brachial VALVE. NAT. SIZE. 



RENSSELAERIA MAINENSIS, new species. 



A medium-sized rensselaeroid form of the shorter ovate type 

 approaching R. sveHsana in contour, but greatly developed at the 

 umbonal end of the pedicle valve. The beak of the pedicle valve is 

 lengthened and .somewhat pointed, as in R. mutahilis,' it is elevated 

 al)ovethe l>eak of the brachial valve by a high pseudo-cardinal area, in 

 which is a triangular delthyrium, open in all specimens preserved. 

 The edges of the delthyrium are bordered by a narrow flattened mar- 

 gin which may be the support of the original deltidial plate or plates, 

 which are wanting in all specimens preserved. These flattened mar- 

 gins of the delthyrium meet at the apex of the delthyrium below the 

 circular foramen, which is nearly terminal. 



The greatest width of the shell is at about one-third distance from 

 the beaks. The average size of mature shells is about one inch in 

 length and a little less in greatest width. 



The pedicle valve is ventricose and in some of the larger shells near 

 the beak is half an inch in depth. The brachial valve is convex and 

 evenly rounded, about one-half as deep as the opposite valve ; neither 

 valve shows any median depression or furrow. The beak of the pedi- 



'Thirteenth Ann. Kept. State Oreologist, New York, 1894. pp. 849 and 850. 



