(sect, e), balanus balanoides. 271 



specimen under var. (a) or under the common form, so that I was 

 compelled to give up var. (a) as a species. 



Monstrous individuals, with the male organs aborted : Parasite. — 

 Amongst some specimens, chiefly elongated ones, sent to me from 

 Tenby, in South Wales, I found no less than seven individuals with 

 some of the posterior cirri distorted, unequal on the opposite sides, 

 and in an almost rudimentary condition, and in each case with the penis 

 truncated, without any muscle entering the stump, which was ab- 

 solutely imperforate : the vesiculse seminales were much shrunk ; 

 in one case without any zoosperms ; in another case with headless 

 zoosperms cohering in an unusual manner ; hence it is certain that 

 these individuals were functionally only female, and could not impreg- 

 nate their own ova ; yet in two instances the ova had been impregnated, 

 no doubt by neighbouring perfect individuals, for they contained well- 

 developed larvae. Several of these monstrous individuals were infested 

 by one, two, or three curious crustaceans, which have been described 

 by Mr. Goodsir,* as the male of the Balanus; but these supposed males 

 are females, and were distended with ova containing almost mature larvae; 

 I believe that they are the females of the unnamed genus, belonging to 

 the family of Ioniens, described by Mr. Goodsir, which live parasitic 

 within the sack (as I likewise found) of the same individual Balani. 



Diagnosis. — I have seen several specimens of this species and of B. 

 crenatus, absolutely undistinguishable in external appearance. I may 

 specify one of B. balanoides, imbedded in an alcyonidium, and one of 

 B. crenatus, imbedded in a sponge, and therefore neither at all abraded. 

 Generally, the tips of the scuta in B. crenatus are a little reflexed, 

 whereas in B. balanoides, when the shell has been at all disintegrated, 

 the tips form a square projection locked into the terga. Bat. crenatus 

 never assumes the punctured appearance so common in B. balanoides. 

 Very young specimens of the latter can be distinguished by their dead 

 white colour and smoothness. The edges of the radii are almost always 

 smoother than in B. crenatus, and they are never so wide as is some- 

 times the case with B. crenatus. When a specimen is disarticulated, 

 our present species can at once be distinguished from B. crenatus (and 

 from B. improvisus), by its membranous basis, and by the solid or 

 cancellated walls, which are rarely permeated by regular tubes or pores ; 

 and the walls when porose are not internally ribbed. I have already 

 pointed out the few very trifling points, in which the opercula of the 

 two species differ. The mouth and cirri offer likewise very few differ- 

 ences: in B. balanoides there are often more teeth on the labrum than 

 in B. crenatus; the rami of the first cirri are perhaps here rather 

 less unequal; the second and third pairs of cirri are certainly in 

 most cases more equal in length ; and lastly, the segments of the sixth 

 cirri, even in the common varieties, bear, in equal-sized specimens, more 

 pairs of spines than in B. crenatus. We shall see that in habits, with 

 regard to depth, the two species differ, B. balanoides inhabiting much 

 shallower w r ater than B. crenatus. 



Range, Habits, fyc. — This species is extraordinarily abundant within 



* ' Edinburgh New Philosophical Journal, 5 July, 1843. 



