CHAPTER XVI. 



The following report upon the Leeches collected by the expedition, 

 and committed to me for examination, is mostly extracted from a Synopsis 

 of the Fresh Water Leeches of North America in the Annual Report of the 

 United States Commissioner of Fish and Fisheries for 1872 and 1873, upon 

 which I was engaged when the specimens were received, and in which, 

 through the courtesy of Lieutenant Wheeler, I was permitted to include the 

 results of a study of his specimens. 



The following artificial key has been prepared in order to facilitate the 

 identification of the genera. It is intended to apply only to the North 

 American genera. 



Analytical hey to the genera of North American Fresh-ivater Leeches. 



a. Head tapering, continuous with tbc body (b) : 

 aa. Head dilated ; neck constricted (A) : 



b. Ocelli marginal in a curved line: no proboscis (c): 



bb. Ocelli in one to four pairs along the median line; an exsertile 



proboscis Clepsine. 



bbb. Ocelli none ; uo proboscis Liostomum. 



c. (Esophagus with folds, and armed with three convergent jaws (d) : 



cu. (Esophagus with folds; no jaws (/): 

 d. Jaws with denticles (e): 



dd. Jaws without denticles Democedes. 



e. (Esophagus with 9 folds ; jaws prominent Macrobdella. 



ce. (Esophagus with 12 folds ; jaws small Aulastomum. 



eee. (Esophagus with G folds ; jaws broad Hirudo. 



f. Folds; 12; transverse lobes ; ocelli, 8 or 10 Semiscolex. 



ff. Folds, G ; 3 transverse lobes ; ocelli 10 Hexabdella. 



fff. Folds, 3; no transverse lobes ; ocelli G or 8 (g) : 



g. Body distinctly dilated and flat posteriorly ; ocelli, 8 ... Neplielopsis. 

 gg. Body not much dilated posteriorly; subdepressed ; 



ocelli, G or 8 Neplielis. 



k. Body subterete ; no lateral appendages (;: 



hh. Body somewhat depressed ; a row of pulsating vesicles along 



each side Cystobranchus. 



i. Head obliquely attached, dilated; margins not fringed Ichlhyobclclla. 



it. Head en m pan n I ate; margin fringed with minute bristles . . . .Astacobddla. 



957 



