TJic Diatoms of Nebraska loi 



and nodules, the upper with pseudoraphe and no nodules, both 

 transversely punctate-striate ; interzones with a narrow marginal 

 fenestrated septum or none ; cells living in masses beside but not 

 upon one another, usually epiphytic on other algae. One auxo- 

 spore is formed asexually from a single cell. The following de- 

 scriptions of species are taken mostly from Schonfeldt, Diat. 

 Deutsch., Oest., und ScJizv. 

 A. With a narrow hyaline space in the middle of the valve. 



b. With a distinct marginal ring on lower valve. i. C. placoitula. 



bb. Without distinct marginal ring on lower valve. 2. C. pedicultis. 

 AA. With wide hyaline space in the middle of the valve. 



3. C. disctilns. 



1. Cocconeis placentula Ehr. Inf., p. 1^4. 1838. 

 PI. 13, figs. 500-504. 



More or less broadly elliptic; upper valve with narrow pseudo- 

 raphe, lower valve with distinct raphe not reaching to the ends ; 

 striations of the upper valve finely granular, the granules forming 

 undulating longitudinal lines, striations extending to the margins 

 of the valve ; lower valve with a distinct broad marginal ring 

 marked with fine granules, striations extending to the marginal 

 ring; length 12-35 /a, width S-20 fi, striations 15-25 in 10 /a. 



Epiphytic on filamentous algae : Andrews, Bellevue, Broken Bow, Calla- 

 way, Cedar Creek, Cherry County, Clear Lake, Crawford, Dewey Lake, 

 Dismal River, Dunning, Emmett, Fremont, Grand Island, Hackberry Lake. 

 Holt County, Hyannis, Lodi, Long Lake, Long Pine, New Helena, New- 

 port, Oakdale, Omaha, Pelican Lake, Red Cloud, St. Paul, St. Michael, 

 Scottsbluff, Seneca, Snake River, South Bend, Thedford, Trenton, Val- 

 entine, Watts Lake, Whitman, Willow Lake. 

 Fossil: Greeley County, Hay Springs, Loup City, Merriman, Valentine 

 Belvidere, S. Dak. ; Fresno, Cal. ; Ft. Collins, Colo. ; New Concord. 

 Ohio. 



Var. intermedia has very coarsely punctate striations on the 

 upper valve, 8-12 in 10 fi. 



In river at Seneca. 



2. Cocconeis pediculus Ehr. Inf., p. ip4, pi. 21, fig. 11. 1838. 

 PI. 13, figs. 505-507- 



Elliptical but in form and size extremely variable, long- or 

 broad-elliptical or almost rectangular with rounded corners, some- 



