[25] ENTOZOA OF MARINE FISHES OF NEW ENGLAND. 477 



Acanthobothrium verticillatum Van Beneden, Bullet. Acad. Belgique, xvi, ii, 79. 



Onchobothrium (Calliobothrium) verticillatum Diesing, Sitzungsb. der Kais. 

 Akad., xiii (1854), 585. Molin, 1. c, xxx (1858), 135, xxxiii (1858), 292, 

 and xxxviii (1859), 10; Idem, Denkschr., xix, 239, tab. v, 3. 



Tetrabothrium verticillatum Wagener, Nov. Act. Nat. Cur., xxiv, Suppl. 85, 

 tab. xxii, 274 aud 275. 



Head continuous, with the subquadrangular body. Bothria four, 

 angular, subelliptical, unequally divided into three loculi by two trans- 

 verse ribs; each bothrium armed with four simple hooks, and provided, 

 in front of hooks, with a trilocular, auxiliary acetabulum, the loculi of 

 the latter arranged in a triangle. Hooks equal and arranged in pairs. 

 Body filiform anteriorly, increasing posteriorly ; anterior segments pro- 

 vided with four triangular, laciniate processes on the posterolateral 

 margin, followed by other segments bearing one, and still others bear- 

 ing two, additional flaps on each postero-lateral margin, subsequent 

 segments with two rounded flaps near posterior, nearly circular in out- 

 line; ultimate segments considerably elongated. Genital apertures 

 marginal. Length To" 1111 to 100 mra . 



. Habitat. — Found at Wood's Holl, Mass., August, 1884, in spiral in- 

 testine of Smooth Dogfish (Mustelus canis). 



In this species there is so much difference between segments occur- 

 ring in different parts of the strobile, that some additional notes are 

 necessary in order to make trustworthy identifications in cases where 

 only fragments are found. The head is so small that it may be easily 

 overlooked by the collector; moreover the anterior segments are so del- 

 icate that, as is often the case, they break and leave the head imbedded 

 in the mucous membrane of tbe intestines of their host. The anterior 

 portion of a living specimen, when isolated from its natural surround- 

 ings and placed in clear water, resembles a very delicate white hair. 

 It may therefore easily escape any but the most careful search. The 

 head itself is only about one-eighth as broad as the head of a common 

 pin, while the breadth of the segments immediately behind the head is 

 about the same as that of a human hair, and the thickness is only about 

 one-third the breadth. The first segments are nearly twice as long as 

 broad, flat and thin, somewhat distinctly four-angled, so that a cross- 

 section is rectangular. The segments are continued at the postero-lat- 

 eral corners into four triangular flaps, which are about one-fourth the 

 length of the segment proper. The posterior margins of the segments, 

 including the flaps, are thick, white, and opaque in life, while the bodies 

 of the segments are'translucent. 



A few segments back from the head the middle of the postero-lateral 

 margin of the segment begins to rise, and soon assumes the form of a 

 third flap. In one specimen, which measured 63 ram in length, this third 

 flap begins about the 3Sth segment. This character continues for sev- 

 eral joiuts until about the 70th segment, when the median flap becomes 

 bifid; at the 80th segment it has become decidedly two-notched, and at 

 the 120th it is divided into two lobes, so that in this part of the body 



