GENUS CORONULA. 409 



much spread out and thin. In C. balmnaris, each rostral 

 muscle consists, in different specimens, of from three to five 

 principal fasciae ; these, at their upper ends, are attached to 

 the cartilaginous plicae at the rostral extremities of the scuta ; 

 at their lower ends, they do not reach (as in all the previous 

 genera) to the basal membrane, but after converging, they 

 diverge again into a little fan of fibres, which are firmly 

 attached to the corium low down on the sides of the sack. 

 The lateral depressores of the scuta consist each of about 

 three fasciae, and they terminate downwards like the rostral 

 muscles. The tergal depressores are spread out into a thin 

 sheet ; upwards they reach to the basal edges of the lips of 

 the sack-aperture, and downwards they curve a little towards 

 the rostral and opposite end of the shell, and extend nearly 

 to the basal membrane. These tergal muscles include two 

 fasciae, larger than the others, which extend rather further, 

 both upwards and downwards, than the other fasciae. 

 But the most novel character in these several muscles is that 

 in their lower portions they do not exhibit transverse striae, 

 thus showing a tendency to become involuntary as in 

 pedunculated cirripedes. This circumstance, and their 

 feebleness, is easily accounted for by the thick unyielding 

 nature of the opercular membrane, and the feebly deve- 

 loped character of the opercular valves. In C. diaclema, the 

 tergal muscles are much spread out, having, as in C. balce- 

 naris, a larger fascia on each side ; but the lateral depressores 

 of the scuta form a well defined nearly cylindrical bundle ; 

 the rostral pair are extremely w T eak and spread out : I 

 could perceive only feeble transverse striae on some of 

 these muscles, and on others there was not the least trace of 

 striae. I may add that the adductor scutorum muscle is 

 well developed, as are the eight pairs of muscles which 

 unite the animal's body to the under surfaces of the scuta. 

 The action of the adductor scutorum serves to close the 

 sack-aperture, but tow r ards the carinal end necessarily with 

 very small force ; protection in this part can only be 

 afforded by the protuberant, valvular lips, and by the 

 dorsal surfaces of the inwardly curled cirri, with their tufts 

 of bristles. 



Mouth. — The mouth (PI. 26, figs. 3, 4) is much elongated. 



