SCALPELLUM. 29 



a narrow ledge of about equal width with the occludent edge, marked likewise with lines 

 of growth, must have overlapped the tergum. Largest specimen 1*15 in length. 



Scutum, Var. II, Tab. II, fig. 9. This valve is narrow, moderately convex, with the 

 upper portion much acuminated; the tergal margin is somewhat hollowed out, and is 

 bordered by a narrow smooth slip, (as in the scutum of S. arcuatuni,) which is simply 

 formed by the thickening from within of the upper part of the valve ; this slip does not 

 reach to the uppermost point. The occludent margin is somewhat arched, at nearly right 

 angles to the basal margin ; lateral margin forming an angle a very little above a right 

 angle with the basal margin. A conspicuous, curved, angular ridge runs from the 

 apex to the baso-lateral angle, (which is not at all protuberant,) and divides the valve 

 obliquely into two almost equal halves. Surface just perceptibly striated, finely and 

 longitudinally. Internally there is a deep pit for the adductor scutorurn, which is situate 

 low down in the valve ; the inner occludent edge in the upper part of the valve {b), above 

 the adductor scutorura, widens suddenly, and is formed into a furrow, which, however, 

 I do not believe to have had any functional importance ; the central internal surface 

 of the valve, above the pit for the adductor muscle, is somewhat prominent ; and a 

 quite small, almost flat, portion of the tergal side is marked by lines of growth, showing 

 where it overlapped the tergum. Altogether there is a considerable resemblance between 

 this valve, both externally, and more especially internally, and that of the Pollicipes 

 Angelini. From the valve being acuminated, with the upper part rather solid, and from 

 the surface being just perceptibly striated, it more probably belonged to var. sulcatum than 

 to the typical S. maximum. 



Scutum, Var. Ill, Tab. II, fig. 10. This third variety, of which the specimen is a fine 

 large one, is about intermediate in outline or acumination between the first and second 

 varieties : the tergal margin is thickened and reflexed as in the first, and is not bordered 

 by a smooth narrow slip as in the second variety. There is no distinct angular ridge, as 

 in the second variety, running from , the apex to the baso-lateral angle. Internally the 

 differences are more conspicuous ; the depression for the adductor muscle is pretty well 

 developed ; a large portion of the upper part of the valve projected freely ; the internal 

 occludent edge, above the adductor-depression, becomes greatly widened and deeply 

 hollowed out, but yet the furrow I believe, as in Var. II, to be of little or no functional 

 importance, and merely a consequence of the internal thickening of the central upper part 

 of the valve ; on the tergal side a wide ledge shows the extent to which that margin 

 overlapped the tergum. The internal surface of the valve, above the adductor-depression, 

 is filled up soUd and is exceedingly prominent, as is the ridge extending from it to the 

 apex ; this ridge, from the unusual width of the internal occludent edge, is pushed over to 

 the tergal side of the valve. 



Professor Steenstrup has sent me two small scuta, collected by M. Angelin at Kopinge 

 and Balsberg, in Scania, which come near to the Third variety; the internal furrow, however, 

 along the occludent margin, is much narrower, deeper, and oblique, so that it is partly 



