322 MEMOIRS OF THE CARNEGIE MUSEUM. 



the lower margin may be almost straight in the middle, and the posterior end may 

 be rounded off. In the female the lower margin projects in the postbasal region, 

 so that the anterior and middle part is almost straight, and the posterior part 

 ascends very suddenly, forming with the part in front a more or less distinct rounded 

 angle, and joining the posterior margin in a very blunt angle. Thus the posterior 

 part of the female shell becomes very high, and in old females this may go to such 

 an extreme that the height of the shell nearly equals the length, thus rendering the 

 outline almost orbicular. In some cases such old females are also much more 

 convex, so that the whole shell approaches the globular shape. 



L. H. D. 



Size: (Males) 1. Portsmouth, Cat. No. 61.4898 103 mm. 75 mm. 61 mm. 



2. Neville Island, Cat. No. 61.2046 100 



3. Kelly, Cat. No. 61.3017 80 



(Females) 4. Industry, Cat. No. 61.3500 (gravid) 92 



5. do. " " do 89 



6. Godfrey, Cat. No. 61.3504 74 



The largest specimen I have seen is from the Clinch River, at Offut, Anderson 

 Co., Tennessee, and measures: L. 104, H. 82, D. 53 mm. It has the shape of the 

 female. 



Soft parts (See Ortmann, 1912, p. 353). Glochidia (See Ortmann, 19116, 

 PI. 89, fig. 22). 



Breeding season: The following records for gravid females are at hand. Aug. 

 10, 1909; Aug. 24, 1910; Aug. 29, 1908; Sept. 8, 1908; Sept. 10, 1908; Sept. 12, 

 1914; Sept. 17, 1908; Sept. 23, 1908. Sept. 8 is the earliest date for glochidia. 

 A female just discharged was collected in Ouachita River by Mr. Wheeler on June 

 26, 1911. 



This is apparently a bradytictic form, beginning to breed in August, having 

 glochidia in September, which are discharged the next spring (June). 



Remarks: This species, when well-developed, is easily recognized by the 

 extremely heavy shell, by the brown color with indistinct raj's, and the general 

 presence of a delicate pink color in the nacre. However, it is very variable with 

 regard to shape. The males, and chiefly the young males, very much resemble 

 Actinonaias ligamentina, so much so in fact, that this species has been placed by 

 the side of L. ligamentina in Simpson's system. Yet there is no close relationship 

 between the two species. Young males of L. orbicidata differ from A. ligamentina 

 by the brown color of the epidermis, and the indistinct and finer rays: however, 

 sometimes the latter species also has a brownish epidermis, and in such cases it is 

 hard to separate them. 



