STATE GEOLOGIST. 11 



The form is more slender than in C. plumicornis. The tracheal 

 vessels are of a different form and color, and the viscera have ob- 

 vious differences. Most conspicuous variations, however, are seen 

 in the shape of the head, which is slender and attenuated toward 

 the insertion of the antennae. The antennae are shortish and have 

 a spine outwardly. The cuticular appendages have an unusual 

 form as has the labrum. The anterior part of the head is 

 spiny. The armature of the end of the abdomen is peculiar. 



The posterior rudimentary appendages are of a different form, 

 and the claws are replaced by club-shaped bodies. A curious ap- 

 pendage below is indicated in the name. The pupa has an extra- 

 ordinarily elongate abdomen which terminates in two paddle-like 

 appendages loosely ciliated outwardly. This species may be called 



Corethra appendiculata, sp. n. 



A New Ectoparasitic Peotozoan. 

 (Plate y. Figs. 12-13.) 



The very strange monocellular animal referred to was found scur- 

 rying over the body of Diaptomus pallidus in a manner like that 

 of a louse scrambling over a bare spot upon its host. The body is 

 disc-shaped and about .04 mm. in diameter. The lower or ciliated 

 side is flat and circular. The upper or aboral portion is convex 

 with an annular depression of greater or less regularity about half 

 way from the center to the margin. The lower side has a chitinous 

 barred ring, corresponding to the depression above, containing 

 about 25 radially arranged bars, each of which, apparently, forms 

 the support for a long cilium which with the others forms a circlet 

 extending beyond the margin. These cilia are used as feet and by 

 them the animal is able to move in any direction, apparently with 

 none of the uncertainty of motion usual to ciliate infusoria. The 

 protoplasm is granular and contains one or more contractile vesicles, 

 one of which appeared very regularly in the center of the chitinous 

 ring before mentioned. These animals can also swim freely, but 

 after a short excursion usually came quickly back, and after 

 shuffling or sliding over the smooth surface of the crustacean as- 

 sumed a position of repose. The generic affinites of this protozoan 



