(sect, d), balanus porcatus. 257 



Var. (a) Walls without longitudinal ribs. Mus. Brit., Cuming, 

 Stutchbury, Jeffreys. 



Hub. — South shores of England, Ireland, Scotland. Shetland Islands, Iceland, 

 Davis's Straits, 66° 30' N. ; Lancaster Sound, 74 6 4S'N. (Mr. Sutherland). 

 Maine and Massachusetts, United States. China (?). In deep water, common on 

 shells, Crustacea, and rocks, sometimes imbedded in sponges. 



Fossil iu the glacial deposits of Scotland, Uddevalla, and Canada ; in the 

 mammalilerous and Red Crag of England ; Mus. Lyell, Sowerby, S. Wood, &c. 



General Appearance. — Shell conical, somewhat convex ; white, some- 

 times tinted yellowish, from the thin investing membrane ; the pro- 

 duced tips of the terga are purple : the parietes of each compartment have 

 from two to four strong, prominent, sharp, straight longitudinal ribs ; 

 these are sometimes irregular, and rarely, as will presently be described, 

 they are absent. The radii are smooth and of considerable breadth ; 

 their summits are nearly parallel to the basis or only slightly oblique : 

 hence the orifice is entire ; it is rather small and ovate, being broad at 

 the rostral end, and very sharp and narrow at the carinal end. 



Dimensions. — The largest specimens which I have seen from Great 

 Britain or Ireland, have been 1*3 of an inch in basal diameter: in 

 Mr. Cuming's collection, however, there was one much depressed spe- 

 cimen from the Shetland Islands, 2'1 in basal diameter: a regularly 

 conical specimen from the coast of Massachusetts attained a nearly 

 equal diameter; out of the glacial- deposits in the Isle of Bute, Scot- 

 laud, several specimens had this same diameter, namely, two inches, 

 and were even more steeply conical, being l'8o in height; some glacial 

 specimens from Uddevalla and Canada, in SirC. Lyell's collection, were 

 1*7 in basal diameter. Hence, it appears, as we shall presently see is 

 likewise the case with B. crenatus and Hameri, that northern specimens, 

 and those from the United States and from the glacial deposits, often 

 exceed in dimensions those from Great Britain or Ireland. 



Scutum : the lines or ridges of growth are broad and prominent ; 

 they are divided into square beads by fine strise, radiating from the 

 apex : and hence the valve is longitudinally striated. Internally, the 

 articular ridge is extremely little prominent ; the adductor ridge, or 

 what must be called such, runs straight down under the articular ridge, 

 making a deep longitudinal pit for the lateral depressor muscle. 

 Tergum : the apex is a little produced, and coloured purple, as well as 

 the upper internal surface of the valve ; there is no longitudinal furrow, 

 only a very slight depression : the spur is placed close to the basi-scutal 

 angle; it is rather long, and measured across the upper part, is half as 

 wide as the valve : its lower end is truncated and rounded ; the basal 

 margin slopes towards it. Internally, a very small portion of the 

 scutal margin is inflected : the articular furrow is shallow and broad : 

 the crests for the depressores are feeble. In young specimens the spur 

 is bluntly pointed. 



The Parietes (4 e) have large square parietal tubes : in the upper part 

 these are filled up solidly without transverse septa: the longitudinal 

 septa are finely denticulated at their bases, and the denticuli extend 



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