T. Davidson — Ujiper Silurian Brachiojooda. 



149 



beak small, incurved, surface smootli. In the interior of the dorsal 

 valve the spirals are narrow anteriorly, but broader on the posterior 

 side, and the principal coils on the posterior side of the spirals are, 

 as in Glassia ohovata, slightly notched or indented, the notch or 

 indentation being in the direction of the end of the spiral, and 

 occupying in most cases the whole breadth of the posterior border. 

 The posterior border of the spirals, including, of course, the notch 

 referred to, slopes slightly downwards on the ventral side towards 

 the anterior margin, and arising from this the notch is partly seen in 

 the ventral aspect of the spirals. This slope of the posterior border 

 of the spirals also accounts for the upper part of the coils on the 

 ventral side being more depressed and less oval than the correspond- 

 ing part of the coils on the dorsal side. 



I here append a restored oxitline sketch of the arrangement of the 

 19 18 



Spiral coils of Glassia obovatot 

 D dorsal, V ventral aspect. 



spiral coils in Glassia ohovata, Fig. 18, from specimens developed by 

 the Eev. N. Glass. The dorsal side of the coils in each spiral cone 

 is somewhat displaced from its natural position in order to show the 

 continuity of the coils. Fig. 19 shows that the coils are not circular, 

 but elongated oval. 



6. Meristella ? or Atrypa ? Maivei, n. sp. PI. V. Fig. 5. 



Shell almost circular, as wide as long, valves moderately convex ; 

 ventral valve rather the deepest, no fold or sinus, but a slight 

 longitudinal groove divides the dorsal valve into two equal lobes ; 

 beak not much produced, with a small circular foramen. Surface of 

 valves marked at intervals by a few slightly projecting concentric 

 ridges. Length 6, breadth 6, depth 3 lines. 



Obs. — A single perfect specimen of this ^hell was found by Mr. 



