20 FOSSIL CIRRIPEDIA. 



and in the fossils from Portugal, it is extremely prominent, and extends down to near the basal 

 margin ; in other specimens it is but slightly prominent, as in those from the Crag (4/) ; 

 it is short, but rather prominent in the specimens (4/^) from Maryland ; Avhereas it is very 

 slightly prominent in the specimens from Virginia. The cavity for the lateral depressor, 

 also, varies greatly ; it is often, as in the recent specimens, bounded on the side towards the 

 occludent margin by a very slight straight ridge, which occasionally folds a little over, 

 making almost a tube ; this, at first, I thought an excellent specific character, but far from 

 this being the case, the cavity often becomes, in recent specimens as well as in the crag 

 specimens (4/), wide, quite open, and shallow. The whole valve in the Crag specimens 

 (fig. 4e) is apt to be more elongated than in the recent or Portuguese specimens (fig. 4/), 

 and especially than in the Maryland (fig. 4/i) specimens. 



Terga very slightly beaked; the surface toward- the carinal end of the valve, in 

 some of the fossil specimens, is feebly striated longitudinally. There is either a slight 

 depression (fig. 4k), or more commonly a deep longitudinal furrow (fig. 4g, 4o) Avith 

 the edges folded in and touching each other, extending down the valve to the spur, and 

 causing the latter to vary in width relatively to its length. When the furrow is closed in, 

 the spur is about one fourth of the entire width of the valve, and has its lower end 

 obliquely rounded, and stands at about its own width from the basi-scutal angle : when 

 there is only a slight depression and no furrow (as is always the case with young specimens, 

 and in the specimens (4k) from Maryland), the spur is broader, equalling one third of the 

 width of the valve, with its lower end almost truncated, and standing at about half its own 

 width from the basi-scutal angle. But the absolute length of the spur, also, varies consider- 

 ably in the Coralline Crag specimens ; it is often very long, (fig. 4g) compared to the whole 

 valve. • In many Italian specimens (4o) it is long and broad. The basal margin of the 

 valve on the carinal side of the spur is sometimes slightly hollowed out ; and when the longi- 

 tudinal furrow is closed, this side slopes considerably towards the spur. Internally, the 

 articular ridge and the crests for the tergal depressor muscles are moderately prominent. 



Parietes, the longitudinal septa sometimes stand near each other, making the parietal 

 pores small. The radii have oblique 'summits, but to a variable degree; their septa are 

 unusually fine, and are denticulated on their lower sides; the interspaces are filled up 

 solidly. The alee have their summits very oblique, with their sutural edges nearly or 

 quite smooth. In most of the fossil specimens (Tab. I, fig. 4b, r), and slightly in some of the 

 recent specimens, the surface of the sheath presents an unusual character, in a narrow, lon- 

 gitudinal, slightly raised border, running along the sutures, on the rostral side of each suture. 



Basis thin, porose ; sometimes with an underlaying cancellated layer. 



All the recent specimens which I have seen, were, with one exception, attached to 

 various shells and crabs, and to each other. The tertiary specimens are often congregated 

 together into great masses. Including the recent and fossil specimens, this species encircles 

 the globe. During the miocene period it seems to have been the commonest existing 

 Sessile Cirripede ; now, it does not appear to be common, excepting, perhaps, at Panama. 



