206 Transactions of the 



puncta large, scattered, diameter of valve ■0064. Fig. 2. Plentiful 

 in a gathering made by Captain Crozier in the Mauritius, very rare 

 in some scrapings from a Haliotis shell, West Indies. 



This very fine and distinct species is easily recognized by the 

 numerous vein-like costae, which become gradually more delicate as 

 they approach the centre, within a short distance of which they 

 disappear. 



Isthmia ? vitrea, n. sp., F. K. — Frustules trapezoidal, the oppo- 

 site corners of the ends more or less produced, hyaline, valves oval 

 or suhorbicular. Shell scrapings. Sandwich Islands, E. M. Browne, 

 Esq., Liverpool. Fig. 3. 



I have placed this curious form in the genus Isthmia with some 

 hesitation, as it wants the characteristic markings of the species 

 belonging to this genus, but the contour of the frustule and mode 

 of self-division resemble the forms belonging to Isthmia more than 

 the species of any other genus with which I am acquainted. I 

 have not been able to detect any markings with the highest power I 

 have access to (Toth immersion by Beck). 



As the subject of secondary markings is of some interest, and as 

 I do not remember seeing those on Isthmia noticed in any work on 

 Diatoms, it will not perhaps be out of place here to give a figure of 

 them. The drawing was made from a fine frustule of I. nervosa 

 from Vancouver's Island. They are easily seen with a J objective 

 and oblique light ; with higher powers they are very distinct. 

 Fig. 4, a, X 600 diameters; h, x 1500 diameters.* 



Nitzsehia ventricosa, m. s., J. L. Palmer. — Frustules linear 

 lanceolate, apices obtuse. Valve with ventral margin convex, 

 dorsum straight or slightly convex, apices very much produced, 

 awn-like, keel submarginal, punctate, puncta reaching to the 

 extremities of the awn-like ends. Striae faint, distant, about 

 13 in -001". Fig. 5. 



Hong Kong, J. L. Palmer, Esq., F.E.C.S., &c., Liverpool. 

 Eio de Janeiro and Bahia, Captain J. Perry, Liverpool. 



This species was first observed by Mr. Palmer in his Hong 

 Kong gatherings ; and it afterwards occurred in great abundance in 

 a sounding taken by Captain Perry off Eio de Janeiro ; it appears 

 to be nearly allied to Nitzsehia rostrata of Smith. (The figure in 

 the Synopsis is totally unlike the form for which it is intended.) 

 I need scarcely say the median line and central nodule are wholly- 

 imaginary, as are also the longitudinal striae; the latter has the 

 keel nearly marginal and the striae very fine, about 60 in "001". 



Nitzsehia deeora, n. sp., F. K. — Valve linear elliptical, some- 



* I think if the aullior of ' The Philoyophy of Evolution ' will carefully 

 examine the markings on a diatom valve, he will admit that nothing is less 

 probable than that they are produced by vibrations on the surface of the mem- 

 branes of these shield-bearing organisms. 



