MANN DIATOMS OF THE ALBATROSS VOYAi . >_ < 



this lack it is a perfectly typical Plagiograninia, and this negative quality is insuffi- 

 cient for separating it. Specimens found in the*following dredging have .1 circular 

 central area and nearly round instead of rectangular or " tesselated " beading, 

 ind al station 2808, < ralapagos Islands. 



DIMEREGRAMMA Ralfs. 



Dimeregramma Ralfs in Pritch. Bist. [nfus. ed. 4. 790. pi I 361. Rabh. 



Fl. Eur. Alg. 1: 13. [2S./.36. L864. Van Beur. Synop. L46. j 1 • 1881 



L885. De Toni, Syll. Alg. 2: 711. L892. Walk. & Chasi N'« t< - on Diat. 1: I. 

 pi t.f.S. L886. Grun. Verh. Zool. Bot. Ges. Wien 12: 377. 1862. Pritch. Bist. 

 loins, ed. 1. 790. pi ../. .. L861. 



Denticula Kutz. in part; Greg. Trans. Roy. S Edinb. 21: i9b.pl 10.J.39. 1857. 



The nearest genus to this isl i 1 >i'h- « 1< -mi- < >v\ .. from which ii differs by the absence 

 of a large central boss. This single characteristic is, however, striking and uniform. 

 Castracane is wrong in Btating thai the only distinction between this genus 

 Denticula Kin/., is thai the former has smooth sides to the valves. Dimeregramma 

 may have the same; bul ii has a pronounced hyaline median line, 'pseudoraphe," 

 dilated at the center, is withoul transverse costae, and has large boss-like elevations 

 at the apices seen clearly in the zonal view), all which distinction's are inapplicable 

 t< 1 Denticula. 

 Dimeregramma inflatum Mann. -p. nov. P ii XLIV, figi re 6. 



Valve seven to eighl times as long as broad, inflated at the center, with bluntly 

 tapering ends; at the apex -1' each a large beak-like process; valves marked with 

 transverse rows of beading, extending from the margin for one-third the width of the 

 valve, leaving ^ median hyaline area, also one-third tin- width of the valve; each row 

 consisting of four beads, the outer largesl and decreasing in size toward the center. 



Length of valve 0.086 nun: width of valve 0.015 nun. 



Type in the U. S. National Museum, No. 590142, from station 2823, Gulf of Califor- 

 nia, April 30, 1888; 26.5 fathoms, bottom of broken shells. 



The in -are>i form to this is D. marinum < rreg. Kali-. '- but I have found it impossible 

 to refer it to that species. Gregory's form has striae with two beads somewhal 

 rated, their line being continued outward to the margin by bars or costae; whereas 

 the moniliform lines in my species begin with very large marginal heads and end 

 inward with Leads "f extreme minuteness. Indeed the whole build of the diatom i- 

 distincl . 



ACHNANTHES Bory. 



AchnantJies Bory, Die. Him. Nat. 1: 79. pi 51. f. :. L822. 



Mcmogramma Ehrenb. Ber. Akad. Wiss. Berl. 1843: 136. I s -! 1. no species, 1854, 



not Comm. 1809. 

 Admanthidium Kiii/.. Bacill. 75. L844: 



Achnanthes dispar Mann. sp. nov. Plate XLIV, figi res 4, 5. 



Under valve headed with minute moniliform striae, transverse until near the ends, 

 then becoming concentric to the points of the apices; the raphe made up of a closely 

 -ei bul moniliform line of exceedingly Bmall head-, at leasl toward its central and 

 terminal portions, and forking near each end into two branches, "tie proceeding to the 

 rounded apex and terminating in a Bmall head, the other and shorter branch running 

 to one Bide and also terminating in a Bmall bead; a narrow hyaline area on either side 

 of the raphe; the transverse, median, hyaline stauros broad and increasing at the 



" Castr. Hep. Voy. Chall. Bot. 2: hi. 1886. 



6 Trans. Roy. Soc. Edinb. 21: 496. pi 10. f. 39. 1857. Pritch. Bist. [nfus. ed. 4. 

 90 1861. Van Beur. Synop. pi 36. /. 9. 1881. De Toni, Syll. Alg. 2: 712. 1892. 



31713— vol i<». pt ."> — 07 8 



