66 MEMOIRS OF THE CARNEGIE MUSEUM. 



there are individuals with indications of another row of tubercles upon the posterior 

 ridge, which is, however, always less distinct than the anterior row. 



Epidermis yellow to dark brown. In young specimens, the color is generally 

 a rather light yellow (wax-yellow), becoming russet or chestnut-brown in older 

 ones. There is no trace of rays. Growth-rests darker than the rest of the surface, 

 but not sharj^ly marked. 



Hinge-teeth well-developed. Pseudocardina,ls moderately large, divergent, 

 ragged. Interdentum moderately wide or narrow. Lateral teeth rather long. 

 Beak-cavity not very deep. Dorsal muscle-scars on the hinge-plate close to the 

 beak-cavity. Nacre white. 



There is not the slightest sexual difference in the shell, and neither the length 

 nor the obesitj^ is connected with the sex. 



L. H. D. 



Size: 1. Kelly, Cat. No. 61.3817 122 nun. SI mm. 50 mm. 



2. Kelly, Cat. No. 61.4.59S (long cf) 108 " 74 " 47 " 



3. Kelly, Cat. No. 61.5506 (long 9 , gravid) 93 " 64 " 43 " 



4. Kelly, Cat. No. 61.3817 (short 9 , gravid) 90 " 67 " 42 " 



5. Godfrey, Cat. No. 61.4.599 (short d') 88 " 72 " 45 " 



6. Shippingport, Cat. No. 61.4600 (long cf) 78 " 58 " 36 " 



Soft parts (See Ortmann, 1912, p. 260, fig. 8). Glochidia (See Ortmann, ibid.). 

 It should be remarked that the measurements previously given were taken from 

 immature glochidia. Gravid females collected subsequeaatly contained fully 

 developel larvse, and according to these, the glochidia measure 0.21 X 0.20 mm. 

 Surber (1912, PI. 1, fig. 12) illustrates them, and gives the size as 0.22 X 0.20 mm. 



Breeding season: I have found gravid females on the following dates: June 

 20, 1911; June 21, 1911; June 22, 1909; July 3, 1908; July 4, 1911; July 13, 1908; 

 July 13, 1911; July 25, 1910; July 27, 1910. Glochidia were observed on July 4 

 and July 25. Thus this species aj^pears to be tj'pically tachytictic, breeding in 

 June and July. Probably the season begins in May, as stated by Surber. 



Remarks: This is a well-marked species, at least in Pennsylvania, character- 

 ized by the shape of the shell, sculpture, and color of the epidermis and soft parts. 

 The most closely allied species is P. cicatricosus, a form not found in Pennsylvania, 

 but farther down the Ohio (nearest point St. Marys, West Virginia). P. cyphyus 

 is distinguished from this species by the more elongated, less oblique shape, with 

 the beaks less anterior, by the sculpture, and the presence of an oblique furrow 

 upon the disk. However, there are individuals, which form, to a degree, a transi- 

 tion between these two species. To these transitional forms belongs U. cicatricoides 

 of Frierson (See above, p, 62), but, on account of the absence of a radiating furrow, 



