14 E. ETHERIDGE, JtjN., ON LOWEH-CAitBOfrltlEEOtTS INVEKTEBKATA. 



many years ago by Captain Thomas Brown as Avicula modioliforme ; 

 but as I cannot distinguish any characters, either external or in- 

 ternal, by which to specifically distinguish Captain Brown's shell 

 from Dr. Fleming's, I propose to adopt the name given by the for- 

 mer as a varietal designation for the thinner and lighter form of 

 M. crassa. To the synonymy already given must therefore be 

 added : — 



Avicula rnodioliforme, Brown, Foss. Conchology, 1849, p. 162, 

 pi. 66. fig. 19. 

 „ „ Morris, Cat. Brit. Foss. 1854, 2nd ed., 



p. 162. 

 „ „ Salter, Mem.'Geol. Survey Scotl. No. 32, 



1861, p. 146. 



A specimen from Fifeshire obtained since my paper was written 

 exhibits another character not hitherto figured, a series of minute 

 pits (? muscular-fibre-pits) running from above the double umbonal 

 anterior muscular scars along the edge of the thickened hinge-area 

 backwards. This is also visible in a specimen from the Water of 

 Leith which has lately come under my notice ; but here the pits 

 are shallower, wider, and further removed from the edge of the 

 hinge-area. 



Log. and Horizon. Forming a bed of shale with ScMzodus Salteri, 

 above and below the shale with marine fossils, at Woodhall, as 

 before. 



Myalina sttblamellosa, sp. nov. PI, I. fig. 15, and PL IT. figs. 16, 17. 



Sjp. cliar. Trigonal ; anterior side small, truncated, with a slightly 

 sigmoidal margin, descending from the beak at rather less than a 

 right angle ; posterior end expanded, flattened, with its margin 

 slightly convex or subtruncate. Hinge-line somewhat depressed, a 

 little less than the width of the shell, the angle formed by the union 

 of the hinge-line and posterior margin an obtuse one. Beaks sharp, 

 terminal, curved anteriorly, with a slightly prominent sigmoidal 

 ridge extending from each down the anterior side and close to its 

 margin ; ventral margin convex. Shell ornamented with concentric 

 lines of growth. 



Obs. This species may be compared with Mytilus Flemingii, 

 M'Coy *, Myalina lamellosa, De Kon. f, Myalina perattenuata, Meek 

 and Hayden J, and M. meliniformis, Meek and Worthen § ; but its 

 greatest affinity is with the first two of these. From Mytilus Fle- 

 mingii it may be distinguished by possessing a smaller and more 

 truncated anterior end, the bounding ridge from the beaks being less 

 posterior in position, a less-depressed and shorter hinge-line, and a 

 more broadly rounded ventral margin. From Myalina lamellosa, 



* Synop. Carb. Foss. Ireland, p. 76, pi. xi. fig. 29. 

 t Anim. Foss. Terr. Carb. Belgique, p. 126, t. 3. fig. 6. 

 I Geol. Rep. Illinois, v. p. 582, t. xxvi. fig. 11. 

 § Ibid. ii. p. 343, t, xxvii. fig. 3. 



