ORTMANN: monograph of the naiades op PENNSYLVANIA. 315 



Sexual differences of shell strongly marked. In the male, the lower margin 

 is more regularly convex, joining the posterior margin in a blunt posterior point, 

 and the outline of the shell is more regularly elliptical. In the female, the lower 

 margin is considerably expanded in the posterior region, sloping up very strongly 

 to the blunt posterior end, so that the posterior part of the shell is higher and more 

 broadly rounded. 



L. H. D. 



Size: (Males) 1. Selinsgrove, Cat. No. 61.4894 122 mm. 80 mm. 51 mm. 



2. Duncannon, Cat. No. 61.3416 11.3 " 74 " 41 " 



3. Yardley, Cat. No. 61.3417 80 " 50 " 32 " 



(Females) 4. York Haven, Cat. No. 61.4893 96 " 71 " 44 " 



5. South Waverly, Cat. No. 61.4003 (gravid) 91 " 67 " 46 " 



6. Yardley, Cat. No. 61.3417 (gravid) 70 " 52 " 36 " 



Soft parts (See Ortmann, 1912, p. 352). Glochidia, ibid, (the latter not fully 

 known, only immature individuals having been observed) . 



Breeding season: Gravid females were observed on the following dates: Aug. 

 13, 1908; Aug. 14, 1908; Aug. 14, 1910; Aug. 20, 1909; Aug. 22, 1909; Aug. 24, 

 1908. Only on the last date were glochidia (immature) found; aU other specimens 

 had only eggs. But just these meagre facts establish the beginning of the breeding 

 season in August, and very probably this species agrees with the allied forms, and 

 is hradytictic, discharging the glochidia in the subsequent spring or early summer. 



Remarks: An exceedingly well defined species, easily recognized. Neverthe- 

 less great confusion prevails with regard to it. This confusion is principally due 

 to the fact that De Kay (1843) misunderstood this and some aUied species, and 

 that the two sexes of cariosus were regarded as different species by other authors 

 (Gould-Binney, and Hartman & IMichener). Simpson (1895) tried to straighten 

 out the confusion, but unfortunately copied two old erroneous figures, and com- 

 mitted an additional error, and thus it has happened that even some recent authors 

 (Conner, 1909, and Caffrey, 1911) confused this species with L. ochracea. 



L. cariosa is allied to the western L. ovata ventricosa, but is smaller than the 

 latter, in the male sex is more regularly elliptical, has hardly a trace of a posterior 

 ridge, and is entirely and characteristically different in color and color-markings. 

 The bright and hght yellow of the epidermis and its high gloss are entirely different 

 from the greenish-olive tints of L. ovata ventricosa, and the restriction of the rays 

 (if such are present) to the posterior section of the shell is also characteristic. Of 

 course, these characters are best seen in young or medium-sized individuals, while 

 in older specimens the smoothness disappears, and the color becomes more dirty: 

 n evertheless even in very old shells the light yellow is generally present at least on 



