iUT. 1-'. A NEW CESTODE FROM SHAEKS — LINTON. 15 



species of selachians ever serves as the final host of this cestode the 

 fact is not indicated by any of the data at hand. On the contrary, 

 sufficient numbers of these hosts were examined in the months of 

 July, August, September, October, and November without finding 

 any adult cestode that could be linked up with this form to make 

 it appear very improbable that P. loliginis can reach the adult stage 

 in any one of these four selachians. 



There is no reason whatever for thinking that P. loliginis ever 

 attains maturity in any teliost. It seems, however, that this larval 

 cestode can resist the digestive juices of a great variety of hosts 

 for some time. Hence it doubtless often happens that, before this 

 larval Phyllohotlirium has reached a true iinal host, such, for exam- 

 ple, as the mackerel shark, or maneater shark, it has sojourned for 

 a shorter or longer time in the alimentary canal of one or more species 

 of selachian, teliost, or squid. It will be noted that P. loliginis has 

 been found in two species of squid on four dates in July and three in 

 August; in four species of selachians on twenty-four dates in May, 

 five in June, four in July, and one in September; in thirteen species 

 of teliosts on fifteen dates in May, ten in June, and nine in July. 



In my notes on the examination of fishes of the Woods Hole region 

 I find records of squid as food in 45 species of fish in which P. 

 loliginis was not found. In 10 of these species examinations were 

 made in May, on seventeen dates; 4 species were examined in June, 

 on six dates ; 6 species were examined in July, on seven dates ; 18 

 species were examined in August, on thirty-one dates; 19 species 

 were examined in September, on thirty-five dates; 11 species were 

 examined in October, on nineteen dates ; 2 species were examined in 

 November, on two dates. 



The adult cestode which is described in this paper was found in 

 but two hosts, Carcharodon carcharias, and Isw'us dekayi, both be- 

 longing to the family Lamnidae, or mackerel sharks. 



Evidence which points to Phyllohothrium tuniidum as the probable 

 adult stage of P. loliginis is based on the similarity in form and de- 

 tails of structure of the scolex. In making this comparison the 

 terminal sucker of P. loliginis is interpreted to be an evanescent, 

 larval structure, as in Scolex yolyniorphus. 



The feature which presents the greatest difficulty is that part of 

 the scolex which is posterior to the bothria. In P. loliginis there is 

 a rather conspicuous neck portion which is sharply marked off from 

 the strobile proper. In P. tumidulum the strobile appears to begin 

 close to the bothria, although segments do not make their appearance 

 at once. In the structure of the bothria and auxiliary suckers, and 

 in the axial portion of the scolex, there is close agreement. 



