12 



PROCEEDINGS OF THE ACADEMY OP 



in both directions towards the median line, crossing as in Hyalodiscus subtilis. 

 (Bailey). coarser than the transverse. These characters are constant in all 

 the specimens I have of this species, from this and other localities. Wolf- 

 boro, N. H., Duck creek, Del. river. 



Stauroneis. This genus is very abundantly represented, particularly in 

 the Wolfboro mud. It is common in all post tertiary deposits, and presents 

 a bewildering looseness of character. 



I have long tried to understand the meaning of S. Baileyi, (Ehr.) and its 

 varieties. Some time ago, I came to the conclusion, that the one having the 

 quadrangular shape and terminal inflexion of St. acuta was a sporangial 

 var. of that species; and that the other (Pteroidea) bore the same relation 

 to St. phenicenteron. This belief has recently been shaken, by my finding the 

 latter variety (Pteroidea) in the " Nova Scotia" deposit, with a very strongly 

 marked terminal inflexion, and the other characters of size, striation, and 

 outline, so variable as to compel the conclusion, that they are both inter- 

 changeable varieties of a common species possibly St. phenicenteron. 



A very interesting study of these forms is afforded, by the Nova Scotia, 

 Blue Hill pond, (Me.) and, in fact, by nearly all the northern deposits, recent 

 and fossil. 



Stauroneis legumen, (Ehr.) The aberrant variety, (pi. ii., fig. 14), will 

 show the range of outline in this species. Frustules of this shape occur 

 sparingly in the Wolfboro mud, along with the ordinary form. 



Stauroneis amphicephala, (Kutz.) This species I notice, to direct atten- 

 tion to the figure of S. anceps in Prof. Smith's "Synopsis," which, in all re- 

 spects, answers to the description and figure of Kutziug's (Bacillarien, p. 105, 

 pi. 30, fig. 25). S. amphicephala. S. anceps, (Ehr.), is subcapitate with truncate 

 apices, S. amphicephala, capitate with rounded ends. Very likely, these two 

 species are identical. The mere length or relations of the stauros to the 

 margin not constituting a valid reason for keeping them apart. 



I cannot close what I have to say about Stauroneis and its varieties, without 

 alluding to a stauroneiform tendency which seems to prevail in certain locali- 

 ties. This is marked in the Wolfboro, where seven species of Stauroneis co- 

 exist with a number of stauroneiform varieties of Navicula. 



I now pass on to notice some varieties of 



Himantidium and Eonotia. I have before spoken of the prevalence of these 

 genera in the Saco and cotemporarj' deposits, and likewise of the remarkable 

 subordination of their specific character to the mctamorphic force, as exempli- 

 fied in Himantidium pectinate , and H. arcus, Eunotia robusta and E. incisa. I now 

 give a few illustrations of the most common of these metamorphic varieties, (pi. 

 ii., fig. 12, 13, etc.) which strongly corroborate the view entertained by the 

 late Prof. W. Smith, of the probable common derivation of many of the known 

 British species of Himantidium, from two types ; viz. : II. pectinate and H. arcus. 

 (vide Synopsis, vol. ii., p. 11). 



Of these varieties, pi. ii., fig. 13a, represents a common sporangial form of 

 Himantidium undulation. It will be seen that the dorsum is already hollowed 

 out as a preliminary step towards another common variety (sporangial) of 

 the same diatom* of which variety I have figured only the extreme and last 



stage, at pi. ii., fig. b. This last, represents quite nearly two conjoined frus- 

 tules of H. undulalum (type), as does the intermediate variety, two of H. 

 pectinate. 



Whether or no these remarkable sporangial frustules ever undergo trans- 



*(Those slides prepared by Mr. Samuels, of Boston, labelled Himantidium undulatum, afford a 

 very fine illustration of this variety, which is abundant in fresh water streams throughout Massa- 

 chusetts) 



[Jan. 



