[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, xxxili (1858), 292, 
and xxxviili (1859), 10; Idem, Dankaain: Xix, 239, tab. v, 3. 
Tetrabothrium verticillatum Wagener, Nov. Minds Nat. Cur., xxiv, Suppl. 85, 
tab. xxii, 274 and 275. - 
Head continuous, with the subquadrangular body. Bothria four, 
angular, subelliptical, unequally divided into three loculi by two traus- 
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 postero-lateral 
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 75™™ to 100™™. 
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 the intestines of their host. The anterior 
portion of a living specimen, when isolated from its nataral 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, 
te the flaps, are thick, white, and opaque in life, while the hose 
of the segments are translucent. 
' A few segments back from the head the middle of the postero- darenat 
margin of the segment begins to rise, and soon assumes the form of a 
third flap. In one specimen, which measured 68™" in length, this third 
flap begins about the 38th segment. This character continues for sev- 
eral joints until about the 70th segment, when the median flap becomes 
bifid; at the 80th segment it has Benes decidedly two-notched, and at 
the 120th it is divided into two lobes, so that in this part of the body 
