476 Transactions of the Society. 



XIII. — Note on the Bev. G. L. Mills' Paper on Diatoms in 

 Peruvian Guano. By F. Kitton, Hon. F.E.M.S. 



(Read Uth June, 1882.) 



In the last volume of the Journal, p. 865, Mr. Mills has figured 

 and described a new species of Auliscus, A. constellatus. After 

 reading his description and carefully examining his excellent 

 figures, I was satisfied that his species was identical with that 

 described by Herr Janisch in his ' Zur Charakteristik des Guanos/ 

 Breslau, 1861-62, as A. Stockhardtii ; it is also figured in 

 Schmidt's ' Atlas der Diatomaceen-Kunde,' Tafel xii. figs. 11-13. 

 Schmidt remarks that fig. 13 = "A. racemosus Ralfs (Gre- 

 ville Monograph of the Genus Auliscus, T.M.S. vol. xi. 1863, 

 p. 46, pi. iii. fig. 18) doch Janisch's Benennung ist alter." This is 

 undoubtedly correct, and Ealfs' specific name must be deleted. 



I communicated the result of my examination to Mr. Mills, 

 who at once admitted the correctness of my views, and, moreover, 

 had the kindness not only to send me the specimens of his sup- 

 posed new species, but also most generously gave me his specimen 

 of Aulacodiscus Kittoni with fourteen processes. On examining 

 this I congratulated myself on possessing a probably unique but 

 certainly a very beautiful state of this species. Examining it again 

 a few days afterwards, I found, in consequence of the balsam being 

 still soft, that a valve of Aulacodiscus Comberi had partially slipped 

 over it. I resolved upon remounting it, and succeeded in placing it 

 on another slide ; during the process I caught a glimpse of the 

 /. v., which induced me to examine it again very carefully with a 

 binocular and \ objective, when to my disappointment I found that 

 our supposed fourteen processed A. Kittoni was composed of the two 

 inner valves (each with seven processes) of a double frustule ; these 

 were in close proximity — in fact, the two convex surfaces touched 

 each other, the elevations on one surface fitting into the concavities 

 of the other, thus accounting for the fact, noticed by Mr. Lewis, 

 that the processes appeared " all in the same plane, and all equally 

 and distinctly defined." The number of processes in Aulacodiscus 

 and Ewpodiscus are now generally admitted to be of no specific 

 value, but it is more constant in some species than in others, e. g. 

 A. formosus. I have never seen more than four processes, and on 

 some valves I have observed as few as three, but in every case they 

 were abnormal forms. In all other species the number is more or 

 less variable. In a pure and recent gathering of A. Kittoni I have 

 seen no valve with more than six processes, four being the usual 

 number, but abnormal forms are by no means rare. I have seen a 

 six-rayed valve with four of the rays at right angles to each other, 



