294 BALANIDJS. 



of growth approximate, moderately prominent ; on the tergal half of 

 the valve, two distinct rather broad furrows, with sometimes a third, 

 and even a fourth, nearer to the occhident margin (PL S, fig. 6 a), 

 extend from the apex down the valve, and give it a very peculiar 

 appearance : the furrows near the tergal margin are the deepest. 

 Internally, the upper part of the valve is roughened with small 

 points : the articular furrow is unusually wide : the articular ridge is 

 very prominent and but little reflexed, with the lower end almost 

 abruptly cut off: the adductor ridge is prominent, but short : there are 

 small deepish pits for the rostral and lateral depressores. 



Terga (6 b), broad, flat, with a slight narrow prominent rim 

 along the scutal margin, which margin is slightly bowed. The basal 

 margin on the carinal side of the spur slopes so gradually towards 

 the spur, that the latter is barely distinct, and is very short, not 

 depending nearly half its own width beneath the basi-scutal angle : 

 it is broad, namely, measured across the upper part, as broad as 

 half the valve ; its basal end is obliquely rounded off on the carinal 

 side ; it is placed close to the basi-scutal angle. The carinal margin 

 of the valve is just perceptibly bow r ed, and is formed by rectangularly 

 upturned lines of growth. Internally, the upper part of the valve is 

 rough ; the articular ridge is prominent ; the crests for the tergal 

 depressores muscles are moderately well-developed. 



Parietes, not porose ; internally, the ribs are smooth, with their basal 

 edges very finely or barely denticulated. The radii (as already stated) 

 are of variable breadth ; they have their upper margins either very 

 slightly or highly oblique, but always smooth and rounded : their 

 sutural edges are quite smooth, or sometimes, with a strong lens, traces 

 of transverse striae, representing septa, can just be discovered. The 

 alee have their upper margins very oblique ; their sutural edges are, in 

 the large specimens, quite smooth ; in the younger ones, plainly 

 crenated; the recipient furrow being clearly marked with these teeth. 

 Basis plainly porose. 



Varieties. — It is certain that there are longitudinally plicated speci- 

 mens of this species, and that the obliquity of the upper margins of 

 the radii also varies a little: nevertheless some of the deeply plicated 

 specimens undoubtedly have a very different aspect from the ordinary 

 varieties, and do really differ in the sutural edges of the aire being 

 crenated, and in the greater narrowness and obliquity of the radii; but 

 these points are all commonly variable. I have not seen any large 

 specimens of the variety, plicatus, so as to compare them with the large 

 specimens of the normal form, yet I can hardly entertain any doubt, 

 considering their agreement in so many important points, that I have 

 rightly treated these forms as mere varieties ; it is unfortunate that none 

 of the specimens of the var. -plicatus seen by me have had opercular 

 valves, as their presence would have removed all shadow of doubt. 



Affinities : this is a strongly characterised species, and nearly allied 

 only to the following species, B. dolosus. The furrows on the scuta in 

 some degree resemble those on B. Icevis, but there is no alliance 

 with that species. It is certain that amongst recent species, the chief 

 affinity is with B. Humeri and amaryllU. 



