Il6 REPORTS ON INVESTIGATIONS AND PROJECTS. 



On June 2, before my arrival at the laboratory, a 9-foot shark was captured. Its 

 spiral valve was opened and placed in 5 per cent formaldehyde. Upon examining this 

 material I decided that it had come from a tiger-shark. As this is an unusual method 

 of identifying a fish it may be worth while to record my reasons for having confidence 

 in this identification. In the first place, the valve itself is of the same type as that of 

 the tiger-shark. This fact, however, does not exclude the cub-shark, which is common 

 in these waters. In the second place, the varied contents of the stomach (see table) 

 agree with what has been recorded for this species (U. S. Fish Commission Bulletin for 

 1899, PP- 270, 271, 425). 



Again, there were a large number of both adult and young and free ripe joints of the 

 singular cestode Thysanocephalmn crispum. In all the tiger-sharks which I have 

 examined in the Woods Hole region I have found this parasite abundant and varying 

 from young specimens a few millimeters in length to adults with ripe segments and 

 measuring as much as a meter in length. There were also large numbers of ripe pro- 

 glottides free in the chyle of the intestines. Furthermore, I have never seen this ces- 

 tode, in its adult stage, in any other host than the tiger-shark. 



Since tiger-sharks are rather common in the waters about the Tortugas this vicarious 

 identification is probably correct. 



In like manner the finding of the cestode Discocephalmn pileatum in the cub-shark, 

 while probably not justifying a change in any record of habitat, at least calls in ques- 

 tion the validity of a former identification. 



This species was based on four specimens obtained from material brought to the 

 laboratory of the United States Fish Commission at Woods Hole, Massachusetts, July 

 19, 1886, and taken from what was reported to me to be a dusky shark (Carcharhinus 

 ohscurus). The viscera only were brought to the laboratory. C. ohscurus is common 

 in the waters about Woods Hole, but C. platyodon has not been recorded from any point 

 so far north. 



The following reasons are given for thinking that the host of the type specimens of 

 D. aieatum may not have been C. ohscurus. 



The first and only find of this species at Woods Hole was the one upon which the 

 genus and species were founded. No other entozoa were found associated with them. 

 In all other specimens of dusky shark which I have examined at Woods Hole I have 

 found numerous cestode parasites. As a rule there were several different species, 

 usually represented by numerous examples, in each shark. The same conditions were 

 found to prevail in the dusky sharks which I examined in 1901 and 1902 at Beaufort, 

 North Carolina. 



The second find of D. pileatum was made in 1903 when I collected seven specimens 

 from a cub-shark (C platyodon) in Bermuda. In that case also the worms were not 

 associated with any other cestodes, and the heads, as in the first instance, were firmly 

 attached to the walls of the intestine. These conditions were repeated very closely in 

 the cub-shark which was examined at Tortugas. The single specimen of D. pileatum 

 was firmly attached to the intestinal wall, the disk-like head being embedded in the sub- 

 mucosa. There were, however, associated with this specimen, five other minute cestodes, 

 representing four species and as many genera. They were Anthohothrium laciniatum, 

 Phoreibothrium lasiuni, Otobothrium crenacolle, and another which was not identified 

 at the time of collecting and concerning whose systematic position I am not yet certain. 



Leaving the species D. pileatum out of the account, it will be observed that two of 

 the above species, viz, A. laciniatum and P. lasium, have been found in the dusky shark, 

 both at Woods Hole and at Beaufort, and one other (O. crenacolle) at the latter place. 

 While there is hence established a close resemblance between the cestode parasites of 

 C. obscurus and C. platyodon, I am still of the opinion from the data thus far at hand 

 that some doubt must rest on the dusky shark's being a host of D. pileatum. 



