Chydorus faviformis. 307 



Material collected in 1893 from northern Wisconsin by Mr. L. 

 'S. Cheney contains specimens which leave no doubt of the spe- 

 cific identity of this form with P. hastatus. 



Chydorus faviformis, sp. nov. 

 Plate XIII, Figs. 7, 8. 



Female. — The form is in general similar to that of C. 

 '■sphc&ricws. The shell of the head and body is covered with deep 

 polygonal cells, formed by outfoldings of the outer layer of the 

 valves. These give the shell an appearance like a honeycomb, 

 whence the specific name. The postabdomen is broad, the end 

 rounded and the anal projection large. There are 9-10 post-anal 

 teeth. The terminal claws are serrate and bear one basal tooth. 



This species is transparent and yellowish. Length, 0.5-0.(5 mm. 



Found in shallow water in the lakes at Minocqua and at Twin 

 lakes, Wis., and in Gogebic lake, Mich. This remarkable spe- 

 cies was first seen at Minocqua, where nast shells were found 

 and afterwards living specimens in abundance. The main pecu- 

 liarity of the species is the development of the deep pits on the 

 surface of the shell. These are identical with the structures 

 occasionally seen in other species of Lynceidoe. Leydig ('60 

 p. 224) says of Pleuroxus trigonellus: "Als etwas besonderes fiel 

 mir noch auf, dass bei der Seitenlage des Thieres (und unter 

 starker Vergroesserung) auf der Woelbung des Kopfschildes sich 

 ein eigenthuemlicher, zarte 1 ", senkrecht'gestellter Hautsaum hin- 

 zieht, ungefaehr auf der Mitte des ScheiteJs beginnend und bis in 

 der Herzgegend sich erstreckend. " 



Schoedler ('63, p. -15.), noted the same fact. P. E. Mueller 

 {'68, p. 190.), observed the same structure in this species and 

 also in P. personatus, in which he figured it (P. IV, f. 23.), and 

 showed that it consists of hexagonal cells corresponding to the 

 reticulations. Kurz ('74, p. 68.), correctly explained and fig- 

 ured it in P. trigonellus, (P. Ill, f. 5). Hellich ('77, p. 104.), 

 noted it in P. trigonellus. Matile ('90, p. 54.), described the 

 occurrence of the "Cuticularsaum" in P. trigonellus, p>ersonatus 

 and aduncus, and in Chydorus sphoericus. 



