MARYLAND GEOLOGICAL SURVEY 175 



Description. — " Parietes, but not basis, permeated by pores; shell 

 white; radii with their oblique summits rough and straight; scutum with- 

 out an adductor ridge ; tergum with the spur rounded." " Under the last 

 species [Balanus porcatus] I have shown that the porose parietes, but 

 solid basis, distinguish this species easily from all the others, with the ex- 

 ception of B. porcatus, from which it can readily be known by the charac- 

 ters of its opercular valves, as already thereunder stated. Judging by 

 external appearances alone, which ought never to be trusted to in the 

 identification of any sessile cirripede, this species might easily be con- 

 founded with Bal. dolosus, found fossil in the same deposits." 



" This species presents a great diversity of external aspect ; I have had 

 figured (Tab. I, Fig. 6a) one of the commonest appearances presented by 

 it; but frequently the shell is quite smooth and depressed, or extremely 

 much elongated and cylindrical, or even club-shaped. The oasis is gen- 

 erally thin and slightly furrowed in lines radiating from the center, but 

 is not permeated by pores ; when, however, in large and old specimens it 

 becomes thicker, as in Tab. I, Fig. 6c, its edge is very distinctly pitted 

 by little hollows, which might sometimes be easily mistaken for the ori- 

 fice of pores : the absence of pores is a very important character in the 

 diagnosis of B. crenatus. The basis is less firmly attached to the sup- 

 porting surface than is usual with most cirripedes, and consequently it 

 often separates from it together with the parietes. With regard to the 

 opercular valves (6d-6g) drawn from recent specimens, I need here 

 only state that the most conspicuous characters are the large articular 

 ridge to the scutum, and the reflexed apices of all four valves, though 

 this latter character is highly variable." 



" The largest recent British specimen which I have seen was only .55 

 of an inch in basal diameter : specimens from Greenland and the north- 

 ern United States, frequently attain a diameter of three-quarters of an 

 inch, and I have seen one single somewhat distorted specimen actually 

 1.6 of an inch in basal diameter. Where individuals have grown crowded 

 together, their length is often twice, and even occasionally thrice as 

 great as their diameter ; thus I have .seen a recent Greenland specimen 

 1.6 of an inch in length, and only .75 in diameter. This species, in its 



