196 S. J. JOHNSTON. 



As is usual in this genus the body is very elongated and 

 flattened. The anterior part of the body is very thin and 

 delicate, and in the region of the ventral sucker is deeply 

 concave. All the specimens are about 12 mm. long, and 

 find their greatest breadth at the level of the gonads where 

 they are 0*809 mm. wide. Just behind the cirrus sac the 

 body is only 0*326 mm. wide, and gradually increases down 

 to the level of the gonads. At the middle of the body the 

 width is 0*632 mm. Behind the testes the body narrows 

 to a blunt, rounded point. Down to the hinder end of the 

 cirrus sac the integument is armed only with fine spines, 

 but behind that level the body is covered with transverse 

 rows of closely placed, thick spines which give it a trans- 

 versely striped appearance. The spines stand very close 

 together, without measurable interval and have the form 

 of almost cubical blocks with the free end produced into a 

 backwardly directed point. They gradually increase in 

 size up to the level of the ovary and behind this point 

 gradually fade away. At the middle of the body they are 

 0*021 mm. thick by 0*018 mm. high, while at the level of 

 the ovary they are '027 mm. thick. 



The head-collar is comparatively 

 poorly developed but bears a row 

 of conspicuous spines round its 

 border. There are twenty-four of 

 these spines, the largest along the 

 lateral border measuring 0*069 x 

 Fig. 6.— Head collar and 0*015 mm. On the ventral side 



spines of Himasthla harrisorvi. rf ^ ^^ ^ ^^ fa ^^ x 



0*015 mm. In addition to the spines round the border the 

 ventral angles bear each four spines arranged in two pairs : 

 two large and two small. 



The oral sucker is very small; it is spherical in shape and 

 has a diameter of 0*085 mm. The ventral sucker lies about 



