134 SUPPLEMENT TO THE 



we cannot say positively whether or not it was provided with spiral appendages ; but in 

 all probability it had none. (See the description of the species at p. 13G of Silurian 

 Monograph. 



Merista (?) CYMBULA, Bav. Sil. Mon., p. 204, PL XXII, figs. 28, 29. 



It would be very desirable that the spirals and their attachments in this species 

 should be examined. 



(?e;22^5— Rhtnchonella, Fischer, 1809. 



Atrypa (?) DEPRESSA, Sow. Dav., Sil. Mon., PI. XIT, figs. 11—15, and PI. XIII, 



fig. 6. 



This has been determined by Mr. Glass not to be a spiral-bearing species. It 

 possesses the interior characters of a Rhynchonella. 



Rhinchonella (?) Pentlandica, Ilaswell. Dav., Sil. Mon., PI. XXII, figs. 9 — 19. 



The exterior characters of this very interesting small species were fully described at 

 p. 187 of my * Silurian Monograph.' I was also able to give a complete description and 

 figure of the interior surface of the dorsal and ventral valves, but was unable to ascertain 

 whether the shell was or not possessed of spiral lamellae for the support of the labial 

 appendages. Unfortunately the species, although extremely abundant, occurs generally 

 only in the state of internal casts or of impressions of its exterior, but it might also be 

 possible to find examples in a suitable condition for working the interior. The muscular 

 impressions bear much general resemblance with those observable in Bayia navicula, 

 and in external shape the shell approaches much to that of Zy(jospira anticostiensis. It 

 is provisionally left in Mhjnchonella, or until its true characters can be determined. 



None of these species can be classed in their proper genera until their internal 

 characters shall have been worked out. There would be no difficulty in attaining that 

 object if a sufficient number of specimens to be operated upon could be got together. 



