40 PROCEEDINGS OF THE NATIONAX. MUSEUM. vol. fi4. 



Carcharhinus milberti. 



1922, August 5 : 1, in spiral valve of a 210-centimeter shark. 

 Cestracion zygaena. 



1911, July 5: Numerous, in spiral valve of a hammerhead shark, 

 measuring 305 centimeter in length. 



1913, July 21 : Few, in spiral valve of a 225-centimeter shark, col- 

 lected by Dr. G. A. MacCallum. August 1 : 62 found in spiral valve 

 of a 195-centimeter shark, and 12 in a 225-centimeter shark ; maxi- 

 mum length about 12 mm. August 18 : Many, from spiral valve of a 

 285-centimeter shark. 



1914, August 7:1; not noted at time of collecting, but found later 

 on a slide with specimens of Phoreiobothrium pectinatum collected 

 on this date. 



(U.S.N.M., Helm. Coll. 7690.) 



This species is readily distinguished from P. cervinum by its 

 smaller size, the two costae, instead of one, on the bothria, and the 

 larger size of the spines on the neck. Dimensions of specimen mounted 

 in balsam: Length, 12 mm.; breadth of scolex, 0.30: length of 

 hooks, 0.10; breadth of pair of hooks, 0.21; maximum length of 

 spines on neck, 0.03; length of posterior proglottides, 1, breadth, 0.5; 

 free proglottides, length, 2.24, breadth, 0.84; length, 2.10, breadth, 

 0.48. 



In the lot collected July 5, 1911, mature free proglottides were ob- 

 served which supply some details of the anatomy not given in the 

 descriptions of this species which have been published. 



The free proglottides, while presenting a considerable variety of 

 shapes, are in general more or less oval in outline, the anterior end 

 being free from genitalia. The cirrus is relativly large and covered 

 with rather stout hooks. The distal portion of the vas deferens is 

 enclosed in the inner end of the cirrus-pouch, the inner coils lying on 

 the median line a little in advance of the vagina. Testes fill practi- 

 cally all of the inner portion of the proglottis. The vagina opens 

 in front, and a little to one side of the cirrus at the genital pore, 

 which is a little back of the middle of the margin ; it passes directly 

 to the median line, where it turns posteriorad and continues as a 

 relatively large vessel, the seminal receptacle, to about the anterior 

 edge of the ovary where it narrows and becomes the germ duct, which 

 is more or less coiled and can be traced, in whole mounts, to the shell 

 gland. The ovary is at iho, posterior end of the proglottis and 

 occupies about half of the space behind the genital pore. The vitel- 

 laria form a layer surrounding the testes and are conspicuous in 

 whole mounts along the lateral margins. 



