338 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lu 



has arisen of giving systematic supremacy to either peristomial 

 configuration or jaw structure. As the latter is at least apparently 

 fixed and invariable regardless of condition of the animal, I have 

 made it the basis for recognition of a subgroup which contains two 

 homognathous species, one with distinct peristomial tentacles, the 

 other with a complete and entire peristomium. 



A brief history of the described forms: The first member of this 

 group to be named was called Astacobdella philadelphica, bj^ Joseph 

 Leidy in 1851. The description (the fu'st validation of a name for 

 an American branchiobdellid) was drawn largely from living speci- 

 mens, and is fau'ly detailed. We can extract information on size, 

 shape, peristomium, and jaw structure, and arrive at the impression 

 of a worm which is essentially similar to recently acquired topotypical 

 specimens from Philadelphica. In 1912, Max M. Ellis described 

 specimens of a similar species from Colorado under the name Cam- 

 barincola macrodonta, making the separation largely on the basis 

 of differences in the form of the peristomium — lobed or "crenulated" 

 in philadelphica but entu'e in macrodonta. 



Subsequently, in 1919, Ellis discussed variation in philadelphica, 

 following the study of a considerable volume of material from his 

 own collections in the midwest and those accumulated at the U.S. 

 National Museum. Working with a much broader species concept 

 than we now know to be justified, Ellis considered philadelphica 

 to be a widespread, variable species, with the variation affecting both 

 dental formula (in small details) and degree of lobation of the peris- 

 tomium. Ellis believed that the normal lobes of the upper half of the 

 peristomium could be extended or retracted at will by living animals, 

 and that the size and shape of the lobes, varying from none to distinct 

 tentacles, was likewise subject to the vagaries of preservation. 

 Material identified as this species indicated a geographic range from 

 New York to Wisconsin, and south to Kentucky and North Carolina 

 (remarkably enough, almost identical with the present range of the 

 species in its restricted sense). 



In the same paper, Ellis described a species under the name 

 Cambarincola chirocephala, based on specimens from Missouri in 

 which peristomial lobes are present as in j^hiladelphica, but the 

 jaws unequal in size — the dorsal jaw from 1.5 to 2 times as wide as 

 the ventral. In this paper, Elhs also published locality records for 

 his species macrodonta from a number of widely scattered western 

 states. Subsequent restudy of this material shows that Ellis has 

 confused several species. Most of his specimens were either immature, 

 overstained, or mounted flattened so that little more than the jaws 

 could be seen. 



