454 PROCEEDINGS OF THE ACADEMY OF [1894. 



ridges on which they rest are largely formed, as shown in fig. 26, of 

 a muscular network derived from the circular fibres. 



In somites VII and VIII a complete transverse loop is developed 

 on the intestine, which is otherwise as in P. alcicoruus. The jaws are 

 also very similar, but diflfer in the shorter median pair of teeth, and 

 the stouter form of the basal plate. These distinctions are ex- 

 aggerated in the figures owing to the fact that they are represented 

 in slightly diflferent positions, fig. 2a being somewhat foreshortened. 



The spermatheca is slender and clavate, and regularly tapers fi'om 

 blind end to mouth. It lies to the left of the intestine. The cop- 

 ulatory bursa is nearly spherical, with thin muscular walls, and 

 larger bursal glands than P. alcicorniis. Its inner surface is thrown 

 into deep ridges, among which the penis lies. The whole structure, 

 when evaginated is shaped not unlike a mushroom, and resembles the 

 corresponding parts of Bdellodrllus philadelphicus. The glandular 

 atrium is remarkable in being divided by a deep cleft into two simi- 

 lar lobes, the structure being flattened in a plane perpendicular to 

 this cleft, giving the organ a shape much resembling the conven- 

 tionalized heart. The penis sheath is short, and lacks a sacular 

 dilation. 



The anterior nephridial pore is on the crest of the ridge of the 

 Ilird somite. In other i-espects this species resembles P. alcicornus. 



The largest example (from which the dissection fig. la was made) 

 from among upwards of fifty specimens measured 1.5 mm. in length, 

 the usual size being about 1 mm. 



Some small cocoons which may belong to this species were found 

 attached to the setae at the bases of the thoracic appendages of the 

 crayfishes from which the specimens were obtained. Unfortunately 

 the animals were not discovered while yet alive. 



P. distichus was found in great numbers with Bdellodrllus phila- 

 delphicus, B. vianus n. s., and Branchiohdella iastabilla upon speci- 

 mens of Cambarus bartonii, from western New York, for which I am 

 indebted to the kindness of Mr. Albert E. Lewis. 



