326 DESCKIPTTON OF [Polygastriccl. 



deficient of the margin frimaj and suture of Navicuh, and the 

 central aperture appears too small. Length 1 -2300th. Massachusetts. 

 BiBLAEiUM Lamina. — Lateral valves widely linear, rounded at 

 the ends, sliglitly constricted in the middle; suture absent; pinnules 

 seven to eight in l-1152nd. Oregon. 



B. Lancea. — Lateral valves lanceolate ; apices subacute ; pinnules 

 parallel, three to eight in 1-11 52nd. Sutui'e wanting. Length 

 1 -336th. Oregon. Ehrcnberg has met with twenty-seven valves 

 concatenated. 



B. lineare. — Lateral valves naiTowly linear, rounded at the ends or 

 subacute; not contracted at the middle; striae lax, strong, four to 

 eight in 1-1 152nd. No suture. Length 1 -552nd. Siberia and Oregon. 

 B. Rhombus. — Lateral valves ovate, rhomboid, quadi'ate ; apices 

 subacute ; median angles more obtuse ; stiise lax, six to eight in 

 1-1 152nd. No suture. Le'ngth 1 -864th. Siberia and Oregon. Some 

 examples are met with having more acute median angles. 



B. speciosum. — Lateral valves elongate, turgid at the centre and at 

 each end; broader on the ventral surface ; one extremity frequently 

 subacute, the other more obtuse ; pinnules sti^ong, but lax ; suture 

 obsolete, not altogether absent. Striae four to eight in 1-1 152nd. 

 Length 1 -336th. Oregon. 



B. Stella. — Lateral valves quadrangular, unequally sinuated, hence 

 a crucial outline ; striated ; ends obtuse ; strite parallel, lax ; sutm-e 

 absent. Length 1 -696th. Oregon, Siberia. 



Genus Campylodisctts. — Valves equidistant, (not concave) ; indi- 

 viduals (frustules) solitary, or temporarily, during self-division, in 

 pairs ; disciform ; tortuous or saddle-shaped ; elliptic, sub-orbicular ; 

 striated, striae mostly radiate. 



Further views of this genus are enunciated in the description of 

 C. ITorologium. 



Campylodlscm is a member of the family Surirellem, of Kutzing ; 

 it api^roaehcs Jfe^sw-fls {Gallionelh, 'Ehx.), but differs in having an 

 elliptic instead of a circular disc. 



"The species, (says theHev. ^Y. Smith) included under this genus, 

 may all be recognized by the characteristic bend or contortion of 

 their surfaces, which gives to the frustule, under certain aspects, the 

 semblance of a miniature saddle. Kiitzing has indeed removed from 



