ORTMANN: monograph of the kAIADES OF PENNSYLVANIA. 191 



green shades prevailing. There is sometimes a Hght (browTiish) ground-color, 

 with the rays not very strongly marked, but generally the dark green raj's prevail, 

 and often the whole shell becomes dark gi'een or blackish. The rays do not possess 

 a strong tendency to break up into spots, and are generally straight and simple, 

 but of various widths. Distinct spots are rarely seen. The posterior slope is 

 rarely lighter than the rest of the shell, and if so, the contrast is not well-marked; 

 but, on the contrary, the posterior slope often appears slightly darker than the 

 rest of the shell, which is due to a stronger development of dark green rays upon it. 

 Nacre whitish or bluish-white, very often with salmon, pinkish, or purplish shades, 

 which, however, are not very intense. Otherwise the shell is like that of A. 

 marginata. 



The female shells are slightly more swollen in the region of the posterior ridge. 

 In old shells, this swelling is sometimes very distinct, and goes so far, that the 

 lateral faces of the shell, in front of the ridge, appear flat or even concave, which 

 concavity corresponds to a slight emargination of the lower margin. ^^^ However, 

 sometimes males also show a slightly concave margin, and in many cases the sex 

 cannot be positively recognized by the characters of the shell, since not all females 

 have that swelling, and since the latter is sometimes also present in males. 



Distance of beaks Pr.ct. of 

 L. H. D. from anterior end. length. 



Size: 1. Ridley Creek, Cat. No. 61.4680 (cf) 70 mm. .38 mm. 29 mm. 18 mm. .26 



2. Kunkletown, Cat. No. 61.4671 (9) 69 " 36 " 26 " 17 " • .25 



3. do. " " do. id') 62 " 36 " 22 " 17 " .27 



4. Greencastle, Cat. No. 61.4675 (cf) 61 " 33 " 24 " 17.5" .29 



5. Carlisle, Cat. No. 61.5873 (9 gravid) 55 " 31 " 22 " 14 " .25 



6. Mt. Dallas, Cat. No. 61.4266(9 gravid) .45 " 26 " 18 " 12 " .27 



7. Mantz, Cat. No. 61.4253 (cf) 45 " 25 " 18 " 12 " .27 



8. do. " " do. (9 gravid) 36 " 23 " 15 " 10 " .28 



There is another specimen from Ridley Creek, which is even larger than No. 

 1 (L. 75 mm.), but it is greatly deformed and freakish in shape, so that the dimen- 

 sions are entirely abnormal. 



The above figures show the more anterior location of the beaks, although 

 the highest value corresponds to the lowest in A. marginata. 



Soft parts and Glockidia identical with those of A. marginata. 



Breeding season: Gravid females have been found: Aug. 9, 1910; Aug. 10, 

 1910; Aug. 11, 1910; Aug. 12, 1910; Aug. 13, 1908; Aug. 13, 1910; Aug. 14, 

 1910; Sept. 4, 1909; Sept. 5, 1909; Sept. 6, 1909; Sept. 8, 1909; and May 3, 

 1909. 



"^ The concave lower margin is here decidedly more frequent than in A. marginata. 



