6 Transactions of the 



II. — Remarks on Aulacodiscus formosus, Omphalojoelia versicolor, 

 &e., with Descri])tion of a Neiv Species of Navieula. 



By F. KiTTON, Norwich. 



(Bead before the Eoyal Microscopical Society, June 4, 1873.) 



Plate XXI. (Lower portion). 



In the April part of the Journal I noticed the fact of the discovery 

 of certain forms of Diatomaceee living in the harbours of Pern 

 and Bohvia, which had previously only been found in guano or fossil 

 deposits. Through the kindness of my friend Captain Perry, of 

 Liverpool, who sent me portions of his gatherings, I have been 

 enabled to study some of the species in a more perfect state than 

 when obtained from guano or fossil deposits. 



The gatherings were procured from the following localities : 

 Iquique, Pisagua, Islay, and Callao in Peru, and Antofagasta in 

 Bolivia, and from depths varying from 20 to 32 fathoms. The 

 Iquique gathering was principally remarkable for the number and 

 beauty of the specimens of Aulacodiscus formosus. I have 

 frequently seen as many as a dozen valves and frustules in a single 

 a lip of the cleaned material, and I have no doubt I am within the 

 mark when I state I have examined over a thousand specimens of 

 it. This form, unlike most other species of the genus, seems to be 

 subject to little variation (excepting size my largest specimen is the 

 7,V, and my smallest ^^q of an inch each in diameter) ; in no case 

 have I detected a valve with more or less than four processes ; even 

 in an abnormal valve, in which the processes occupy only half the 

 disk, there are still four of them Plate XXI. (lower portion), 

 Fig. 1. Mixed with this species I occasionally noticed a disk re- 

 sembling Greville's figure of A. infatus, but on comparing it with 

 authentic specimens of that species I found they were not identical : 

 further examination showed them to be recently-formed valves of 

 A. formosus ; many of the frustules when allowed to dry. and then 

 placed in a drop of distilled water, split, the valves becoming 

 detached from the cingulum, and I noticed in several instances that 

 the frustule separated into three valves, the outer valves being of the 

 usual dark blue colour, whilst the internal one was hyaline, the 

 granules were also smaller and more distant. The detection of 

 the separation of the newly-formed valves is of great interest, and 

 forces upon us the conclusion that many so-called new species are 

 only valves of known species in various stages of development ; it at 



EXPLANATION OF PLATE XXI. (Lower portion). 



Fig. L — Abnormal form of Aulacodiscus formosus. 

 „ 2. — Ideal yoction of valve of A. formosus. 

 „ 3.— Abnormal forms of A. inarijantdcciis. 



