OF DENISON UNIVERSITY. 53 



GENUS MONOSTYLA, Ehr. 



Shell depressed, oval ; head opening large, notched before and behind. The 

 foot has two short basal segments and a long terminal one ending in a small spine, 

 hence appearing as though bearing one long spine. The eye is single and situ- 

 ated at the base of a large ganglion. The maxtax is large and quadrate. The 

 viscera are simple. 



MoNOSTYLA (quadridentata, EJir. ?) 



Two species of Monostyla have been thus far encountered, one of 

 which may be identical with M. quadridentata of Ehrenberg. The 

 body is bell-shaped or inverted pear-shaped, the oral margin being 

 produced into two sickle-shaped spines turned outward, which are dis- 

 tinct from the acute margins of the shell itself. The body is com- 

 posed of two segments or apparent segments, the second being small 

 and conical. The terminal joint of the foot is slender and elongate, 

 bearing a thorn-like spine. The ganglion is very large. The maxtax 

 is also large and opens into a sack-like alimentary canal not evidently 

 subdivided. The shell in this species is ornamented with granules. 

 Length of lorica, .15 mm., width, .11 mm., terminal caudal joint, with 

 spine, .08 mm. Found in June, in Minnesota. 



A second species is smaller, measuring from .11 to .12 mm., foot 

 .04 to .08 mm., width, .11 mm. The shell is smooth and the curved 

 spines are absent. 



The following species are known : — 



Monostyla lunar is, Ehr., M. cornuta, Ehr., M. closterocerca, 

 Schm., M. oophthalnia, Schm., and M. macrognatha, Schm. 



GENUS DISTYLA, Eckstein. 



Shell ovate conical, closed behind, except for the small opening admitting the 

 foot. In front, the opening is wide and guarded on either side by projecting an- 

 gles. The foot is one-jointed and bears two equal, divaricated spines. The 

 shell may be smooth or ornamented with raised lines and serrations. The eye is 

 single and seated upon a considerable ganglion. Two species are described by 

 Eckstein from Europe {D. gissensis and D. ludioigii) and two additional ones occur 

 in America. 



DiSTYLA MINNESOTENSIS, Sp. 11. 



This is a large species, .25 mm. long, with a pear-shaped body of 

 two segments, the first being .20 mm. long and of equal width. The 

 second segment is .05 mm. long and has an oval slit behind for the in- 

 sertion of the foot and permitting its free lateral motion. The claws 



