ANNELID GENUS CAMBARINCOLA — HOFFMAN 273 



and distributions concerning evolution in the group as well as the 

 possible routes by which branchiobdellids settled the North American 

 land-mass. I suspect that the worms came to this continent probably 

 in late Cretaceous times on primitive astacine crayfish from eastern 

 Asia, and that these crustaceans may have spread eastward across the 

 continent — giving rise to the more specialized cambarine genera in 

 eastern North America rather than in Mexico as postulated by students 

 of the Decapoda. The present discontinuity in the distribution of 

 Cambarincola, and the isolated, relict status of its most primitive 

 forms, are thought to be the result of fragmentation of the old habitat 

 conditions by climatic changes in the late Tertiary. 



Acknowledgments 



This stud}'' of Cambarincola was made at the suggestion, and under 

 the sympathetic guidance of Dr. P. C. Holt. I take great pleasure in 

 acknowledging the extent of his personal interest and concern in 

 facilitating and furthermg my investigations, always more in the role 

 of longtime friend than that of major professor. The work was done 

 while I was a candidate for the Ph. D. degree in the Graduate School 

 of the Virginia Polytechnic Institute. Financial support was fur- 

 nished by a research grant (G-4439) to Dr. Holt from the National 

 Science Foundation. 



I am likewise under an obligation to Dr. Fenner A. Chace, Curator 

 of the Division of Marine Invertebrates, U.S. National Museum, who 

 provided working space and the opportunity to study type specimens, 

 and later kindly loaned the bulk of the Museum's holdings in branchio- 

 bdellids for study. 



It is finally necessary to acknowledge the contribution of numerous 

 collectors who have obtained the material with either a direct or in- 

 direct interest in branchiobdellids, particularly Mr. C. W. Hart, who 

 made a special effort to obtain topotj'pes of Astacobdella philadelphica. 



Review of the Literature 



The first American species of Cambarincola to be described was 

 placed in the genus Astacobddla, a group of Palearctic leeches (Leid}^, 

 1851). Since that time, the generic concept has been slowly but 

 progi'essively refined. 



In 1894, J. P. Moore described several new species of branchio- 

 bdellids from eastern United States, and in his paper discussed Leidy's 

 earlier name under the combination Branchiobdella philadelphica, 

 and published an outline drawing of a specimen. The majority of 

 Moore's work on this group involved species of other genera, although 

 in a brief reference in his paper on the leeches of Illinois (1901) he 



