166 Papers from the Marine Biological Laboratory at Tortugas. 
I am inclined to allow considerable variation in the sizes of corresponding 
hooks in different individuals. 
It is, perhaps, worthy of note that, while I have found the encysted stage 
of R. speciosum in several hosts, especially the groupers, both at Tortugas 
and Bermuda, I did not find the adult of this cestode at either place. The 
number of sharks examined was so small, however, that this apparent ab- 
sence of adults is not significant. 
The large number of cestodes in contrast with the small number of indi- 
viduals is significant and agrees with the characteristics, in this particular. 
of tropic fauna in general. 
The multiplication of species of the genus Rhynchobothrium is distaste- 
ful to the writer, but seems to be unavoidable, as will appear when the 
figures of characteristic hooks are consulted. 
It is to be hoped that another season’s collecting will result in the addi- 
tion of sufficient material to permit of a study of the comparative anatomy 
of the proglottides. Reports on the trematodes, nematodes, and acantho- 
cephala will be made as soon as the material can be studied. 
It is a genuine pleasure to acknowledge in this place the unfailing cour- 
tesy and interest shown by the director of the laboratory, Dr. Alfred G. 
Mayer, as well as the assistance which was given so freely by my fellow- 
workers in the laboratory, in the way of supplying me with material for 
study. I am especially indebted to my friend, Dr. Ulric Dahlgren, for 
many valuable favors. 
DESCRIPTION OF SPECIES. 
1. Dibothrium sp. 
(Plate 1, figs. 1 and 2.) 
The only representative of this genus seen was a larval form, a few 
examples of which were found encysted on the viscera of Atherina laticeps, 
June 30. 
The cysts were elongated and filled with yellowish granular plastic 
material, which surrounded the elongated larva. The parenchyma of the 
larva contained numerous calcareous bodies, which were relatively large, 
especially at the posterior end. 
The following dimensions, in millimeters, are of the living specimen: 
Cyst, length 2.8; diameter, anterior 0.47, middle 0.70, posterior 0.35. Larva, 
length 2.60; diameter, anterior 0.32, middle 0.42, posterior 0.28; length of 
anterior part, head 0.30. 
A specimen (fig. 2), which had been fixed over the flame, under pres- 
sure, and afterwards stained with hematoxylin and mounted in balsam, 
exhibits a peculiar glandular structure much like that noted in a Ryncho- 
bothrium from the sand-shark (Proceedings of the National Museum, vol. 
XIX, p. 797, plate 63, figs. 14,15. See also Bull. U. S. Fish Com. for 1899, 
