Dr. E. Woochvard — Cirripedes from Trimmingham Chalk. 343 



" Tergum (Figs. 11-13). — Eather broad, convex ; apex pointed and 

 much curled towards the scuta ; upper carinal margin unusually 

 arched, slightly longer^ than the lower carinal margin; there is 

 a deep depression parallel to the occludent margin, which is itself 

 rounded, protuberant, and considerably shorter than the scutal 

 margin. A curved ridge projecting up above the general surface of 

 the valve, with sloping sides, runs from the apex to the basal angle, 

 which latter is broad and rounded ; ^ the ridge runs down nearly in 

 the middle of the valve." (Darwin, op. cit., p. 76.) 



'^ Scutum (Figs. 14-18). — Almost triangular, moderately convex; 

 occludent margin considerably arched in the upper part and bowed 

 towards the tex-ga ; basal margin not straight, with a short portion 

 close to the rostral angle, forming a rectangle with the occludent 

 margin; the remaining portion, if produced, would form a rather 



Figs. 14-18. — Five scuta of Brachylepas (PoUieipes) fallax, Dar'^vin, sp. 

 size. From the Chalk of Trimmino'ham. 



X 2 nat. 



larger angle with it; hence the baso-lateral portion of the whole 

 valve is somewhat protuberant. The tergo-lateral margin is in the 

 upper part slightly hollowed out, and in the lower part almost 

 straight. A very slightly curved ridge runs from the apex to the 

 baso-lateral angle, which is broad, rounded, and not prominent ; the 

 ridge has sloping, not wall-like sides. Internally the structure of 

 the upper part closely resembles that of P. rigidms. The occludent 

 edge is thickened, broad, and flat, and is marked by lines of growth, 

 and widens towards the apex ; there is a rather deep furrow close to 

 the tergal margin, but there is no trace of a central ridge ; the deep 

 pit for the adductor muscle lies quite close under the furrow and 

 flat occludent edge. The furrow on the tergal side is rather 

 narrower, and a central portion of the inner occludent margin 



^ This does uot hold good in a number of specimens. Thus, the upper carinal 

 margin in fom- specimens measures 8, 9, 10, and 11 mm. ; -whilst the lower margin in 

 the same specimens measures 8, 11, 11, and 10 mm. ; so that the relative length of 

 the margin and also the degree of curvature varies considerably. 



* The basal angle in a number of terga of this species, instead of being broad and 

 rounded, is narrow and rather pointed. I am, however, inclined to consider these 

 only trivial variations and of no real specific importance. 



