158 LEWIS, ON DIATOMACE.li;. 



doxical difficulty is, that possibly the telluric impression of the 

 subjacent soil may continue to make itself felt in the deve- 

 lopment of species for a long period after the other surround- 

 ings have ceased to be favorable. 



At all events, it needs some other explanation than that 

 ordinarily had recourse to, viz., the hardihood of these low 

 forms of organic life, and the agency of birds and fish to 

 account for the permanent localization of marine species at 

 points apparently so unsuited to their existence. 



I. New species and sporangia! forms. 



1. Tricerutium alternans, Bailey, sporangial? — This some- 

 what doubtful form has so few of the characters of T. alter- 

 nans, that, but for the occurrence of intermediate varieties, the 

 propriety of its reference to that species might seem question- 

 able. The structure of the valve is distinctly cellular, in the 

 smaller varieties indistinctly so, and that of the obtuse pro- 

 cesses faintly punctate. The largest pustules attain the size 

 of T. favus. 



Hab. — St. Mary's river, Ga., in scum of a salt marsh. 



2. Surirella pulchra, n. sp. — F. V. linear narrow, often 

 somewhat twisted. V. ovate or elliptical ; alse distinct ; cana- 

 liculi numerous, marginal inflated as in S. fastuosa, 6 in "001, 

 extending for about two fifths of the distance to centre of 

 valve ; central portion smooth, circumscribed on either side by 

 a coarsely striated, arcuate band, with harshly defined edges, 

 and connected with its fellow at a short distance from the end 

 of the valve. Immediately exterior to these bands, and sepa- 

 rating them from the inner termination of eanaliculi through- 

 out the entire length of the valve, is a corresponding, only 

 somewhat naiTOwer, arcuate, smooth space. Length of valve 

 •005 to -009. 



This very beautiful form^ evidently allied to S. fastuosa and 

 S. eximia, ' Mic. Journ.,' differs from both in the greater 

 number of its eanaliculi and the presence of the striated 

 bands. In this respect it closely resembles the species next 

 to be described. 



Hab. — St. Mary's River, Ga., salt marsh and in tidal mud. 

 ^Vharf at Fernandina, Florida, tidal deposit. Pier at St. 

 Augustine, Florida. Rare. 



3. Surirella Febigerii, n. sp. — F. V. as in last described. 

 V. elliptical to linear ovate, sometimes broadly sphenoid ; 

 alse inconspicuous ; eanaliculi 6 a 7 in "001, straight or slightly 

 convex, linear, reaching from the margin to a striated, arcuate 

 band, situated relatively to the valves as in the preceding. 



