392 MEMOIRS OF THE CVRXEfUE MUSEUM 



gives a clue. This, however, is not the case in rerij young specimens, (less than '20 

 nnn. long), and such I am unahle to distinguish from the typical form. 



The characters are slightly variable, as has been pointed out above, but this 

 variet}' generally is ver\' uniform in its characters in Pennsylvania. I have not 

 found any variations worthy of special mention. With reference to the lateral spine 

 of the carapace, there are specimens which show no trace of it, (.young as'well as old). 

 In old specimens this spine is often tuberculiform. and in aljout half of the number 

 at hand there is on each side a sharp, but always small lateral sj)ine. In this respect 

 there is no difference in the specimens of northwestern Pennsylvania from those 

 found in Allegheny < ounty. 



It seems to me that the southern records for this variety (^Maryland, Virginia, 

 and also Kentucky)-^, do not refer to exactly the same forni which is found 

 in the north (( "anada. New York, northwestern Penns^dvania, northern (Jhio). 

 Hay (1890, p. 966), in the key to the species gives as one of the differential 

 characters of C hartoni rohudus : "carapace cylindrical, sides nearly parallel as 

 far forward as cervical groove, then curving abruptly to the base of rostrum," 

 while, under <'. Ixaiofii. the carapace is described as " . . . depressed, sides gently 

 curving toward the fnmt and rear." This cylindrical shaj)e of the carapace is deci- 

 dedly not present in our northern form ; on the contrary, the depression of the cara- 

 pace in our rahiif^fiis is, if anything, more pronounced than in the typical hdiioui ; 

 and our robustus agrees in this respect with ( iii-ard's type from ( 'anada, preserved in 

 the Academy of Natural I'^ciences, Philadelphia, and which has been examined by 

 the writer. 



On the other hand, our s|)eeimens from Kentucky seem to approach the form 

 from ^'irginia and Maryland. The shupe of the carapace is more cylindrical, as 

 Hay describes it, G : H : B = 1 ; l.Oo to 1.2 : 1.2 to 1.3. This .shows that the width 

 of the carapace at the branchial and hepatic regions is decidedh' less, compared with 

 the vertical diameter at the gastric region, than in the typical hdrioiii There are 

 other slight differences in the form from Kentucky : ( 1 ) the rostrum is not quite so 

 narrow ; (2) the lateral spine of the carapace is absent ; (3) the punctures of the areola 

 are not so crowded (about three rows), and are similar to those of hartoni ; (4) the 

 impi'essions of the hand are indistinct; (5) the double row of tubercles on the inner 

 margin of the hand is different, the outer row being distinct, but the inner consist- 

 ing of only a few more or less distinct irregular tubercles. All four specimens from 

 Kentucky are comparatively small, (the largest is 54 mm. long), and thus the two 

 last described characters may be due to age, although the specimens differ slightly 



23 Faxon, 1890; Hay. 1899 ; Williamson, 1905 ; Ortraann, 19056. 



