30 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



BIDDULPHIOIDE.E 

 BIDDULPHIE^E 



(a) Triceratiince. Frustule cylindrical or prismatic, with three or more sides. 



(b) Biddulphiince. Frustule cylindroid; valve with ends elevated into round proc- 

 esses or long horns. 



(c) Anaukce. Valve elliptical, lunate or triangular, with internal septa. 



(d) Euodiece. Frustule cuneate in zone view; valve lunate. 



(a) TRICERATIINCE 



(1) Ditylum. Frustule imperfectly siliceous. Zone with numerous divisions. Valve 

 with central spine. 



(2) Trinacria. Processes with sharp spines. 



DITYLUM BAIL. (1861) 

 (dis, two, and tyle, a swelling, referring to the outline of the frustule) 



Frustule quadrangular, convex at the ends. Valve triangular, with undulating sides, 

 the angles ending in a sharp point surmounted by a bristle. Surface of valve convex at 

 centre from which projects a long stout spine. 



DITYLUM INTRICATUM (WEST) GRUN. 



Valve with the angles separated from the central part by lines imitating septa. Sur- 

 face with radiating lines of fine puncta. 



Blue clay. Rare. 



PL 6, Fig. 4. 



Detached valves only have been found in the blue clay. The form is regarded as but 

 slightly siliceous and, therefore, the zone or girdle not being found in the fossil deposits, I 

 am unable to illustrate it from material in the vicinity. On Plate 38, Figs. 6 and 7, I have 

 sketched the zone and valve views of specimens found recently at Vera Cruz and labelled 

 by H. L. Smith Triceratum intricatum West. I can find no difference between the recent 

 and fossil forms of the valves. The zone is covered with fine puncta in quincunx, not 

 visible under ordinary illumination. 



The form as figured in Plate 6 corresponds to the figure of Lithodesmium undulatum 

 Ehr. in Van Heurck, and West, in describing the Triceratium undulatum Wm. Sm. (figured 

 as T. striolatum), thought that his T. intricatum was distinct from Ehrenberg's form on 

 the ground that the latter came from the "Bermuda" (Nottingham) earth and must be 

 strongly siliceous. Lithodesmium is characterized by the envelopment of the frustules by a 

 cellular membrane which does not appear, evidently, in Ditylum. D. brightwellii is distin- 

 guished by its crown of spines on the margin; otherwise it closely resembles D. intricatum. 



TRINACRIA HEIB. (1863) 

 (treis, three, and acra, a point) 

 Valve triangular, angles elevated into spines. Cells at the margin large. 



TRINACRIA PILEOLUS (EHH.) GRUN. 



Valve with concave sides. Surface concave with unequal punctiform and scattered 

 markings with central dots. Cells at the margin large, rounded. At the angles, which vary 

 in elevation, a few puncta are seen. 



Triceratium pileolus Ehr. 



Blue clay. Rare. 



PI. 6, Fig. 9. 



