part 4] 



CAMBRIAN HORIZONS OF COMLET. 



349 



at an angle of 70° to 80° ; interior showing a bell-shaped cavity 

 connected posteriorly with the foramen by a short groove in the 

 wall of the cavity ; main vascular sinuses deep on each side of the 

 cavity, then disappearing, except in a few instances when they are 

 traceable a long way towards the anterior margin ; cardinal scars 

 large ; parietal band sinuous, connecting the forward ends of the 



Fig. 3. — Acrothyra comleyensis, sp. nov. X about 24. Restora- 

 tion of the interior of the ventral valve. 



[/= Foramen ; p — Minute pit ; b.c. — Bell-shaped cavity ; v.s. = Vascular 

 surus ; M. = Cardinal muscle-scar ; p.b. = Parietal band ; cm. = Central 

 muscle-scar (?) ; a.l.m. = Anterior lateral muscle-scar (?).] 



deeper parts of the vascular sinuses and passing the centre-line at 

 about the half-length ; muscle-scars (?) represented by four slightly- 

 raised prominences almost touching the parietal band ; two little 

 pits occur in the wall of the bell-shaped cavity on each side of the 

 foramen and a little in advance of it. Associated dorsal valves 

 subcircular, convex, with apex depressed and marginal ; interior 

 with a median ridge extending about two-thirds the length of the 

 valve, sometimes interrupted, sometimes only weaker at the middle 

 of its course, from which point two branches diverge slightly and 

 then pass forwards parallel to the median ridge ; main vascular 

 sinuses well developed posteriorly ; cardinal muscle-scars large. 



