ART. 21. PARASITES OF SHAEKS AND SKATES LINTON. 15 



(U. S. N. M., Helm. Coll. 7667-7668.) 



1923. On 4 dates in July and one in August; 3 to 40; few to great 

 numbers of free proglottides; maximum length noted 100 mm. 



NOTES ON CERTAIN GENERA BELONGING TO THE FAIMILY PHYL- 



LOBOTHRIIDAE. 



In common with others who have attempted to classify Selachian 

 Cestodes I have experienced much difficulty with those genera of the 

 Phyllobothriidae which are characterized by having a scolex with 

 four unarmed bothria, each provided with an auxiliary sucker at 

 its anterior end, and without costae. 



The generic names which I have used for members of this group 

 are, Anthocephaluni Linton, Calyptrohothrium Monticelli, Crosso- 

 hothrium Linton, Monorygma Diesing, Orygmathobotlivium Diesing, 

 and Pliyllohothrium Beneden. 



As I have interpreted these genei-a they may be arranged accord- 

 ing to the following scheme : 



1. Auxiliary acetabula relatively small, borders of brothria usually thin and 



flexible, often folded or crumpled 3. 



2. Auxiliary acetabula more or less cup-shaped . 4, 



3. Bothria in pairs, leaf-like with crenulate borders PhyUoJwthrium. 



Bothria cruciform with crenulated borders AnthocephaJum. 



Bothria cruciform, borders not crenulate Crossobothrium. 



4. Bothria with sphincter muscle on border Orx/gmatohothrium . 



Bothria plain, acetalnila cup-shaped Monorygma. 



Acetabula large, horseshoe shape Calyptrobothrium. 



Consideration is not here given to two characters which are usually 

 mentioned in descriptions of these genera, that is, the presence or 

 absence of a myzorhynchus, and the pedicelled or sessile condition 

 of the bothria. 



As to these features it may be said that, whether the bothria are 

 pedicelled or not, is often very difficult to determine in these strongly 

 contractile forms, unless one has seen them when they were actively 

 mobile. Furthermore, the presence or absence of a myzorhynchus, 

 unless it is represented by a permanent sucker, as inEcheneihothrium^ 

 is of little importance, since it is an evanescent structure, found in 

 a variety of larval forms, as for Scolex poJymor'phus^ and may be 

 retained more or less discernibly, in scoleces which have developed 

 strobiles. 



It is significant that Zschokke in his admirable monograph ^ gives 

 evidence of the unsettled state of the systematic relations of such 

 forms as are here being considered, as for example, Orygmatoho- 

 thrium {Phyllohothrium) dohrnii Oerley.and Anfhohothrium{Oryg- 

 matobothimmi) musteli van Beneden ; other examples coidd be cited. 



" Recherch. sur Struct., etc., ties Cestodes. 



