160 LEWIS^ ON DIATOMACE^. 



dilated. Keel or ala central or subcentral, constricted, cos- 

 tate, spathulate at extremities. V. lanceolate or lanceolate 

 with produced extremities. 



The great variation in size, outline, and general configura- 

 tion of the frustules of tliis species, together with the fact of 

 their being so imperfectly silicious that a boiling in weak acid 

 either distorts or entirely destroys the specimen, renders it 

 not improbable that this may be an early developmental form, 

 although of what known species, if any, would be difficult to 

 say. A smooth and very diaphanous variety oi A. paladosa 

 occurs in the same gathering. 



The " plates " alluded to by the late Prof. Gregory {' Ma- 

 rine Diatoma*cei» of Clyde '), as characterising A. lepidoptera, 

 and others of the genus, are strongly marked in this species, 

 and serve as a point of attachment between the various frus- 

 tules. Arising from the surface of the valve at a short dis- 

 tance from its extremity, they are broadly convex and incline 

 somewhat outwards. By the central portion of the outer 

 aspect or margin of these plates, each frustule is united to the 

 adjoining one on both sides, the keels or alse of all three over- 

 lapping for about one half their breadth. A nearly perfect circle 

 is thus often formed by a union of from eight to twelve frus- 

 tules. I am not aware of any description heretofore given of 

 the union of the frustules of Amphiprora into bands or other- 

 wise. In consequence of this arrangement, an end view of 

 the frustule can readily be obtained. 



Hab. — On marine algse (Ceramium) , off Light House Rocks, 

 New London, abundant. The bands of frustules are often 

 moulded around the smaller stems of E-hodospermese. 



7. Amphiprora J^reis, n. sp. — Frustule usually twisted, 

 hyaline, very inconspicuous. F. V. elliptical, with rounded 

 ends, constriction of keel or ala very deep. V. striated, striae 

 from 50 a 60 in '001, extending to margin of ala. Supple- 

 mentary plates ? crenulate or undulating, at the margin 

 appearing as though perforated with small puncta. Length 

 of valve -002 a •OOJ.S. 



Hab. — On algse {Dasya elegans) from a brackish lake at 

 Narragansett. 



This beautiful and delicate little form I have found only at 

 Narragansett. Its very small size and faint markings make 

 it so inconspicuous an object that a l-12th inch is required 

 not only to define but even to detect the balsamed specimens 

 on a moderately crowded slide. The only indication of 

 marking arresting the eye is the lines of puncta or dots 

 seen. These I at first supposed were portions of the ala, 

 but after examining several specimens and fragments of 



