Helminth Fauna of the Dry Tortugas. 173 



laria form a narrow band near the margin, and extend from near the ante- 

 rior end quite to the posterior end. 



Behind the ovaries the segment usually narrows and the only reproduc- 

 tive organs there represented are the vitellaria. 



The uterus lies in the median region between the ovaries and the angle 

 of the vagina. The ova are elliptical, amber-colored, with rather thin shells, 

 and are about 0.023 by 0.013 mm. in the two principal diameters. 



The cirrus is long and slender and is armed with exceedingly minute 

 spines. The cirrus pouch lies in the angle of the vagina, but the vas defer- 

 ens, for the most part, lies in front of the vagina. 



The testes occupy the median portion of the segment in front of the 

 reproductive aperture nearly to the anterior end, and are bordered by the 

 marginally placed vitellaria. 



The extreme anterior end of the proglottis is sometimes rounded and 

 slightly constricted. There is always a short anterior portion which con- 

 tains no genitalia. 



Dimensions of living worm in millimeters : Length 5 to 10 ; head, length 

 0.28, breadth 0.28; diameter of neck o.u ; length of hook 0.064. ^ n a speci- 

 men mounted in balsam the length of a bothrinm was 0.26, its hooks o.io; 

 another, bothrium 0.26, hook 0.07. The base of the hook is here included. 



From the nurse-shark (Giuglimostoma cirratum) , July 15, numerous; 

 July 1 8, several. 



13. Acanthobothrium brevissime sp. nov. 



(Plates 4, figs. 26-29.) 



This specific name is used to accommodate a few very minute cestodes 

 collected from the spiral valve of the sting-ray (Dasyatis say), July 10. 



Bothria with characters of the genus, that is, with two transverse costse, 

 a pair of two-pronged hooks, and a triangular cushion in front of the hooks. 

 The first segment begins at once, without being preceded by any noticeable 

 transverse lines or divisions of any kind, and the following segment is 

 adult, with a well-developed cirrus pouch and relatively large testes. 



In the specimen which was sketched (fig. 26), the enlargement which is 

 shown at the base of the neck is evidently due to contraction. Since this 

 part contains the rudiments of reproductive organs, it is to be regarded as 

 the first segment. 



Dimensions of specimens mounted in balsam, in millimeters : Length 

 1.40; head, length 0.20, breadth o.n ; diameter of neck 0.04; length of neck, 

 from the head to the point where it merges into the body, 0.42; length of 

 last, and, in this specimen, the only segment, 0.60; breadth, anterior o.n, 

 middle 0.12, posterior 0.07; hooks, all more or less broken, about 0.05. 

 The cirrus pouch is at about the middle of the length. 



As these worms were thought at the time of collecting to be small ex- 

 amples of A. paulem, few notes were made of the living worms, and the 



13 



