35.0 BALANIDE. 



are broader and shorter than in the commoner variety ; and the spur 

 more especially is broader. The scutal margin is much more widely 

 inflected, and the articular ridge much more prominent ; consequently 

 the articular furrow is much deeper. 



Structure of the parietes and radii. — The orange or yolk-of-egg 

 colour, which is so conspicuous a character in the present species, is 

 due to a layer of shell between the inner and outer lamina, and is ex- 

 posed only by the corrosion of the latter. Hence the very base of the 

 shell is not of this colour; nor are the uppermost and still more deeply 

 corroded portions, for here the orange-coloured layer has been removed. 

 The sheath is orange-coloured, and the operculum, to a certain extent, 

 is similarly tinted. The epidermis on the parietes, where preserved 

 quite close to the basis, supports remarkably strong spines, about 1 ^th 

 of an inch in length. The basal internal edges of the walls are rather 

 coarsely striated with irregular short ridges and sub-cylindrical points ; 

 and the walls in most of the specimens are regularly and deeply folded, 

 which, with the little ridges, gives the appearance represented in fig. 

 2 b, PL 12. I have stated, under the Genus, that in the corroded and 

 depressed specimens, the walls are rendered extremely thick by the in- 

 ward production and upward extension of these same ridges and points ; 

 the under surface of the shell acquiring almost the appearance of Chelo- 

 nobia caretta. The Radii are often not developed, even the sutures 

 being obscure; when most developed, they are narrow, with the outer 

 lamina along the growing edge sinuous, giving to the sutures a cre- 

 mated appearance. The sinuosities on the growing edge generally send 

 inwards short ridges or septa, like those on the sutural edges of the radii 

 in most Balanidae, but of which there is no trace in the other species of 

 Elminius. In very minute, colourless specimens, about the ^th of an 

 inch in diameter, the radii are quite smooth-edged. The alas have their 

 edges strongly crenated. The lower edge of the sheath depends freely. 



Mouth : the labrum shows some tendency to be bullate ; the notch 

 is broad and shallow : the palpi have a thick brush of bristles on their 

 inner sides. The mandibles have four or five teeth. In the maxillae, 

 the upper spines above the broad notch, are very strong. In the 

 outer maxillae, the two lobes are widely separated. 



Cirri : in the first pair, one ramus is about one fifth longer than the 

 other. In the third pair, the posterior ramus is one fourth longer 

 than the anterior ramus, and its terminal segments are tapering, each 

 having a single circle of bristles : the other segments, and those of the 

 shorter ramus, support many coarsely pectinated spines. In the sixth 

 cirrus, the segments are protuberant in front, and carry four pairs of 

 stout spines, with a tuft of fine bristles between them. 



Affinities.- This species differs considerably from the first two of the 

 genus. In several characters it approaches nearer than the other 

 species to Tetraclita, especially to T. jwrosa ; — namely, in the scutum 

 having an adductor ridge and crests for the lateral depressores, in the 

 whole form of the tergum, in the thick walls liable to much corrosion, in 

 the narrow radii, and in their edges, as well as those of the alae, being 

 crenated ; ami, lastly, in the character of the cirri, more especially of 

 the third pair, with its coarsely pectinated spines. It also approaches, 

 in all its characters, Balaiius bnperator and fosculus. 



