316 DESCRIPTION OF [ Polygastrica, 



Genus Amphipeoha. — It presents the general characters of Pinnu' 

 laria ; but the terminal apertures, instead of occupying the margin^ 

 are placed in the median line. Individuals solitary. 



A. constricta. — Smooth ; constricted laterally at the middle. In 

 general form resembles Navicula alata. Cuba. (P. 15, f. 1.) 



A. navicidaris. — Oblong, transversely striated ; expanded 

 (dilated J on the side, at the middle ; apices obtuse. Has the habit 

 of a Pinnularia. Cuba and United States. 



A. alata, (Kiitz). = Entomoneis alata, (Ehr.) — (P. 16, f. 5, 6, 7.) 



A. puJchra, (Bailey.) — Large, deeply constiicted, ends rounded, 

 sides compressed, carinate, distinctly striate, and near the margin 

 punctate. Central portion narrow, sigmoid, with a few fine longi- 

 tudinal lines. Often contorted, so as to bring one half into a plane 

 at right angles to the other. Long Island, E[u.dson Piver, &c. 



A. ornata, (Bailey.) — " Small, deeply constricted, ends truncated 

 and rounded, sides marked with a longitudinal row of undulations or 

 pininilae, as in Surirella. Often contorted. The ruffle-like rows of 

 pinnulse distinguish this species fi'om all others. It probably has 

 minute striae also, but I did not have an oppor-timity to examine 

 with high powers." 



A. quadrifasciata, (Bailey.) — Small, moderately constricted, ends 

 truncate or slightly rounded ; sides compressed or Carinate, lanceolate, 

 with the apices produced and rostellate. "VYhen living, each specimen 

 was marked by four ti'ansverse yellow bands. A high power shows 

 the surface to be veiy minutely striated. 



Genus Amphora. — Frustules solitary, with two central apertures,^ 

 one on each side the median line, but without terminal ones. 



The double umbilicus is the distinguishing feature by which it 

 differs from the sub-genera of JVavicula. It is a member of Kiitzing's 

 fiimily JSfaviculece. 



A. amlis = Navicula (?) Amphora. — Tui^gid, oval, ends broadly 

 rounded, truncate ; margin closely striated ; and very fine longitu- 

 dinal median lines; striae very fine, nine in 1- 1200th; (1 -456th to 

 1-1 20th.) Fresh water (P. 3, f. 153.) 



A. affmis. — Oblong, narro\ving gently towards the widely truncate 

 ends ; margin longitudinally sti'iped, and very fine longitudinal 

 lines traversing the centre. (l-9G0th to l-390th.) 



