282 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 114 



with increase in size ; smaller species usually remain within very close 

 limits to their average. The range in size in Cambarincola is as great 

 as for the rest of the family, with no particular affinities being re- 

 flected by the development of very large or very small forms, both of 

 which occur in groups unrelated by other characters. Both size ex- 

 tremes appear to occur only in mountainous regions, whereas species 

 of moderate dimensions tend to be widespread in lowland areas. In 

 general, so far as Cambarincola is concerned, body size is often a good 

 specific character, usually associated with other structural features, 

 and is sometimes useful in identification. 



III. Body Ornamentation 



The vast majority of branchiobdellids are basically similar in ex- 

 ternal appearance, but in several forms the segments are provided 

 with dorsal elaborations in the form of fleshy digitiform lobes of 

 various length, or even large median processes which are distally 

 branched. Species so ornamented have traditionally been thrown 

 into the genus Pterodrilus without any consideration of other char- 

 acters, and that "genus" has become a sort of assemblage of incon- 

 gruous forms most of which are quite unrelated. 



In many species the peristomium is produced into four lobes of 

 variable size and length on the dorsal side. These structures reach 

 their maximum development (among American species) in the genus 

 Ceratodrilus, becoming nearly as long as the head. In Cambarincola, 

 lobation of the peristomium occurs in various forms, and has been 

 used and misused in the past for separation of species and subgenera, 

 even though the significance of the character has been misunderstood. 

 Cambarincola philadelphica has been considered by both Ellis and 

 Goodnight to be very variable in this respect, but in actuality the 

 variation ascribed to that species is due to a confusion of several dis- 

 tinct species under one name. Well defined peristomial lobes ("ten- 

 tacles") occur in association with other characters and reflect specific 

 distinctness of worms so endowed. They do not alone indicate rela- 

 tionships, however, for they occur in several groups of the genus 

 Cambarincola as well as in Ceratodrilus and Stephariodrilus. 



IV. Jaws 



Branchiobdellids are the only Oligochaeta having sclerotized 

 moLithparts (in the form of a dorsal and a ventral piece) of variable 

 size and shape, but generally provided with caudally directed denta- 

 tions or cusps on the posterior margins. (The name "jaw" is used 

 only provisionally for the buccal armature of branchiobdellids, with 

 the realization that it is certainly not homologous even with the 

 mouthparts of polychaetes.) Ellis (1919) postulated that the 



