Helminth Fauna of the Dry Tortugas. 165 



collected in 1906, I take this opportunity of recording the cestocles from 

 this species of shark, which is not included in last year's list: 



Crossobothrium angustiim, or near it; 3 scoleces and a few fragments from the spiral 



valve. 



Phorciobothrium lasiiini, 15. from the spiral valve. 

 Otobothrium penctrans, i 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, Pedibothriiiin, 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. pauluin, 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 

 Tetrarhynchidas 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, 



