Development of Traehyneis aspera Cleve. By T. Comber. 401 
divides into two frustules. 1 1 is to the process of development of these 
young inner valves that my remarks will have reference. 
My attention was first drawn to the subject when preparing for 
Dr. Murray lists of the species of diatoms found in certain of the 
‘ Challenger ’ dredgings. In that from Station 145, off Marion Island, 
there occurs pretty frequently a large form of Traehyneis aspera , 
distinguished by Prof. Cleve as var. oblonga ( = Stauroptera oblonga 
Bailey). One frustule, which was in course of subdivision, presented 
a peculiar appearance. The old valves had separated from each other, 
and two new valves had been formed inside of them ; but these had a 
structure evidently different from that of the old valves, and the 
difference was so great as to at once attract attention, even under 
the low power (2/3-in. objective) which was being used, by the 
variation of colour when dry. The two outer valves were grey, like 
those of the other frustules present in the material, but the two inner 
valves vere a bright azure. On this being noticed, the specimen was 
isolated and mounted ; but, in getting rid of an air-bubble, which 
formed within it, it was slightly broken (fig. 1). In one respect 
this was an advantage, for a fragment of one of the inner valves 
became detached, and admitted of closer examination under a higher 
power than was possible when it was enclosed within the connecting 
zone of the frustule. It was found to be thin and flexible, and its 
structure very simple, consisting of parallel costae, with some tendency 
to anastomose (fig. 2). The mature valves are much thicker and 
more robust, and their structure more complex (fig. 5). It exhibits 
more or less elongated areoles, across each of which is a series of fine 
cross-bars, and beneath each a large circular marking, analogous to the 
so-called “ eye-spots,” that frequently occur in the valve of disciform 
species. 
These cross-bars appear to be on the outer surface of the valve ; 
but, if they form an “ exterior stratum,” as stated by Cleve, I have 
never been able to detach it, as a separate layer, from the rest of the 
valve. The “ eye-spots” are on an inner layer, which is readily 
detachable. Schmidt figures such a detached layer, Atlas, plate 48, 
fig. 23, calling it an “ untere Schalenschicht,” and in some gatherings 
such layers are not unfrequent. Fig. 4 represents such an “ eye-spot ” 
layer. 
The valve, no doubt, developes gradually, passing insensibly from 
one stage to another without any sharp division between them ; but 
I will mention those stages which I have actually observed. 
In the first, parallel costae are discernible within the parent 
frustule, but are so rudimentary and ill-defined as to be hardly recog- 
nisable as yet forming a valve. 
The second is that which has already been illustrated (figs. 1 
and 2) and described. 
In the third (fig. 3) the costae, instead of being straight and 
parallel, have become slightly flexuose, the undulations of one costa 
