NATURAL HISTORY SOCIETY OF GLASGOW. 223 



belong, or, perhaps, some of his samples belong to the one, some 

 to the other, and his D. tenuis is probably that of Smith; his D. 

 frigida is refeiTed to the same by Grunow, and as Grunow de- 

 scribes the striae, he must be correct; but specimens which I have 

 seen named by Kiitzing belong to D. inflata, that is, have very 

 faint strise, not visible under a good |-th lens, but when seen with 

 higher powers, are not more close than in D. tenuis. D. thermalia 

 of Kiitzing is also involved in doubt. Some specimens named by 

 Kiitzing, which I have seen, have the strise conspicuous, and 

 belong to D. tenuis, Sm.; others from Puy de Dome have them 

 extremely faint, and are to be referred to I), inflata. Grunow 

 takes no notice of the strise in his short description, but seems to 

 represent them in his figures. D. elegans, Kiitz., as far as I can 

 make out by Grunow's description of the costae and strise, is the 

 same as B. tenuis; it is certainly not D. ocellata of Smith, as sup- 

 posed by Grunow and Rabenhorst. D. suhtilis of Grunow, accord- 

 ing to his figure and description, appears to me to be also a mere 

 state of D. tenuis, enfeebled by growing in brackish water. The 

 shape of the valve, and number of costse in -001, afford no good 

 characters. The latter vary from 8 to 20 in "001; the striae 

 are more constant, being about 40 in "001. 



6. D. ocellata — ocelli conspicuous; costae strong, uniting before 

 reaching the middle (about one-third across the valve), and 

 forming false ocelli, or apparent perforations, then expanding and 

 forming a plate over the rest of the valve; striae fine, reaching 

 about two-tliirds across the valve. The peculiarity of this species 

 is in the costae, after leaving the margin a little way, expanding 

 and forming a plate, but leaving a nearly circular space, bounded 

 by the two costae on each side, between the margin from which 

 they originated, and the place from where they expand. The 

 name was taken, not so much from the ocelli on the F. V., which 

 D. tenuis and D. inflata also exhibit, but from the apparent per- 

 forations (or ocelli) near the one margin of the valve. Such have 

 been seen in no other species. I have seen no specimens, except 

 from the locality mentioned by Smith. 



