158 T. H. Withers—New Chalk Cirripedes. 
margin. Surface of valve ornamented with fine, almost regular, 
longitudinal ridges, rather close together, the interspaces about the 
width of the ridges. Running transversely to these, at regular 
intervals, are about sixteen folds or ridges, which probably correspond 
to the growth-lines. -A prominent ridge extends in a straight line 
from the apex to the basal angle, dividing the valve into two unequal 
portions, the oceludent portion being the broadest. This ridge on. 
reaching about half the length of the valve bifurcates, but with a very 
narrow interspace; the ridge is very little thicker than those on the 
occludent portion, but it is prominent because the carinal portion of 
the valve lies on a lower plane than the rest of the valve, and the 
ridge on the carinal side has an almost perpendicular face. The 
longitudinal ridges, of which there are about eleven on the carinal 
portion, are flattened, the first two or three on the inside being 
bifurcated at their bases, and the interspaces very narrow. ‘Those on 
the occludent portion, numbering thirteen, are sharply rounded, and 
more pronounced, the interspaces about the width of the ridges. 
From the apex to the scutal margin runs a faint groove, from which 
the occludent margin rises up. 
Fie. 14. Scalpellum dissimile, T. H. Withers, sp. nov. External view of left 
tergum, x 4 nat. size. Turonian, Zerebratulina-zone; Gatehampton 
Farm, east of Goring-on-Thames, Oxon. (B.M., I. 8398.) 
Holotype.—A left tergum (B.M., I. 8898), collected by C. P. 
Chatwin & T. H. Withers. The specimen has its basal angle 
slightly broken. Length of valve 7°5mm., breadth 4 mm., length of 
oceludent margin 5 mm., length of scutal margin 3:5 mm. 
Horizon and Locality.—Turonian, upper part of Zerebratulina-zone : 
Gatehampton Farm,’ east of Goring-on-Thames, Oxon. 
Comparison with other Species.—This tergum apparently agrees more 
closely with S. attenuatum, H. Woodward (1906, Gzor. Mae., Dec. V, 
Vol. III, p. 352, Text-fig. 37) than any other species. The holotype 
of S. attenuatum is a tergum from the Senonian (Bel. mucronata-zone) 
of Harford Bridges Pit, near Norwich, and is in the collection of 
Dr. A. W. Rowe, who has kindly lent it to me for comparison. It is 
about three times the size of the holotype of S. dussimile. In 
S. attenuatum the longitudinal ridges, instead of being rounded and 
regular, are much flattened and vary in width on the occludent 
portion of the valve; the majority of those on the inner half are 
1 Description of section, C. P. Chatwin & T. H. Withers, ‘‘ The Zones of the 
Chalk in the Thames Valley between Goring and Shiplake’’: Proc. Geol. Assoc.,1908,. 
vol. xx, p. 394. 
