Helminth Fauna of the Dry Tortugas. 165 
collected in 1906, I take this opportunity of recording the cestodes from 
this species of shark, which is not included in last year’s list: 
Crossobothrium angustum, or near it; 3 scoleces and a few fragments from the spiral 
valve. 
Phoreiobothrium lasium, 15, from the spiral valve. | ) : 
Otobothrium penetrans, 1 adult from stomach. This name was given to an immature 
form found in the flesh of the gar (Tylosurus acus) in Bermuda. This is therefore 
the first record of the adult of this species. 
In the Year Book of the Carnegie Institution for 1906, page 116, I 
stated that the spiral valve of a shark which had been kept in formalin 
until my arrival at the laboratory belonged to a tiger-shark (Galeocerdo 
tigrinus). As the identification was a somewhat unusual one, being based 
in large part on the character of the stomach contents and the entozoa, 
I embrace this opportunity of confirming the identification. Having learned 
from Dr. Mayer that the jaws of the shark in question had been sent to the 
museum of Harvard University, I wrote to Professor Samuel Garman, who 
replies that the jaws are the jaws of Galeocerdo tigrinus. 
In the present paper only the cestodes of the collection are described. 
A more critical study of the material than was possible at the time of 
collecting reveals that the cestodes from the nurse-shark are, for the most 
part, new, as is the case also with a nematode from the same host, a species 
of the genus Acanthocheilus, which will be described in a subsequent paper. 
It has been found necessary to establish a new genus, Pedibothrium, to 
accommodate certain cestodes found in the nurse-shark. This genus is 
represented by three distinct species. 
The species of Acanthobothrium, which was recorded in my notes at the 
time of collecting as A. paulum, proves to be a new species. Several species 
of the genus Rhynchobothrium were found, very few of which could be 
referred to any known species. 
It has long been recognized that the hooks on the proboscides of the 
Tetrarhynchide are indispensable in determining the species. This makes 
it extremely difficult to identify species in this family, since it is frequently 
impossible to get the specimens to unroll their proboscides. Even when the 
scoleces have been made transparent, so that the hooks in the inverted 
proboscides can be seen, it is usually not possible to make out their arrange- 
ment, and unless there is something characteristic in the outlines of the 
hooks, one must often remain uncertain about the species where the everted 
proboscides have not been seen. 
Again, the appearance of a given proboscis at different levels may be 
very different. It follows that species which have been described and fig- 
ured when only the basal portions of the proboscides were seen, may not 
be recognized when examples are seen for the first time with proboscides 
completely unrolled. 
So far as my observation extends, there is little variation in the arrange- 
ment of the hooks in the individuals of a given species, although, at present, 
