28 . FOSSIL CIRRIPEDIA. 



ScALPELLUM MAXIMUM, var. tyiHcum. Tab. II, figs. 1, 4, 5, 8. 



S. carind introrsum leviter arcuatd, latitudine valva altitudinem super ante ; tecto 

 transverse leniter arcuato ; jyarie^i^w^ intra-parietibusque angustis, sujperjicie pane 

 Icevi. 



Carina slightly bowed inwards ; width of valve greater than the depth ; tectum flatly 

 arched transversely ; parietes and intra-parietes narrow ; surface nearly smooth. 



Carina, Tab. II, fig. 1. In this, the typical variety, the carina is very slightly bowed 

 inwards, widening gradually downwards from the apex, of which no part projected freely ; 

 walls rather thin ; tectum very flatly arched, not sub-carinated ; basal margin rectangu- 

 larly or rather more acutely pointed ; parietes very slightly concave, splaying outwards, 

 nan'ower than one side of the tectum, separated from it and from the intra-parietes by 

 rounded ridges ; intra-parietes narrow, not extending baseward so far as the basal margin 

 of the parietes ; width of valve measured from marginal edge to edge, considerably greater 

 than the depth, measured in the same place from the central crest to either marginal edge ; 

 but the width compared with the depth varies a little : inner margin of valve nearly 

 straight. Length of longest specimen {Mus. Fitch) nearly 1^ inch. This variety in the 

 Norwich beds seems about equally common with var. sidcatmn, but the former alone is 

 found in Hanover and in Scania, excepting that in the latter country some specimens indi- 

 cate a passage to the var. cylindraceum. 



Scutum, Tab. II, flg. 8. In Mr. Fitch's collection there are three left-hand valves of a 

 Scalpellum, which, from their size and smoothness, I have no doubt belonged to this species, 

 and from their thinness, probably to the variety of carina considered as typical under the 

 simple name of S. maximum : valve unusually thin and little convex ; trapezoidal, with 

 the apex less produced than is usual in the genus ; broad in proportion to its length, the 

 basal margin being •GO, and the occludent margin '98 in length, therefore the breadth 

 equals two thirds of the length. Basal margin (just perceptibly hollowed out) forming less 

 than a right angle with the (just perceptibly outwardly arched) occludent margin, and 

 forming an almost exact rectangle with the lateral margin ; the latter meets the tergal 

 margin at an angle of about 135°. The edge of the tergal margin is thickened and 

 slightly reflexed ; the upper part of the lateral margin is in some specimens a little bowed 

 inwards. The baso-lateral angle is rounded and just perceptibly protuberant ; no ridge 

 or furrow runs from it to the apex. Internally the depression for the adductor muscle is 

 singularly shallow (fig. 8 c) ; a very small portion of the upper part of the valve projected 

 freely ; the internal surface of the valve, above the pit for the adductor muscle, has not 

 been thickened, and is therefore slightly concave or almost flat. The internal occludent 

 edge in the upper ])art is only a very little widened, and is flat ; on the tergal margin, 



