GENUS — SCALPELLUM. 219 



in all the species ; in the lower whorl there are either 

 two or three pair of latera, in the former case the infra- 

 median pair being absent. The latera differ considerably 

 in shape in the different species. 



The Peduncle is generally rather short, and, with the 

 exception of S. Peronii, is covered with calcified scales. 

 These scales are generally small, and placed symmetri- 

 cally in close whorls, in an imbricated order, with each 

 scale corresponding to the interspace between two scales 

 in the whorls above and below. In S. ornatum, the 

 scales are so wide, transversely, that there are only four 

 in each whorl. In S. villosum, the scales are spindle- 

 shaped and arranged somewhat irregularly in transverse 

 rows, not very near to each other. New calcareous scales 

 originate only round the top of the peduncle, and they 

 continue to grow only in the few upper whorls ; and as 

 the peduncle itself continues to increase in diameter by 

 the formation of new inner membranous layers and the 

 disintegration of the old outer layers, the calcareous scales 

 come in the lower part of the peduncle to stand further 

 and further apart. In the earliest stage of growth there 

 are no calcareous scales on the peduncle in S. vulgare ; 

 they first appear under the carina. Spines are articu- 

 lated in great numbers on the surface of the peduncle in 

 S. vulgar e, S. Peronii, and S. villosicm, and very short ones 

 on that of S. roslratum. 



Attachment, — All the species, except S. villosum, are 

 attached to horny corallines : the singular means of 

 attachment in S. vulgare will be described under that 

 species, and is probably common to several of the other 

 species. The larva in most, or in all cases, when it pro- 

 ceeds to attach itself, clings head downwards to the 

 branch, and hence the capitulum comes to be placed 

 upwards, with its orifice fronting the branch and the 

 carina outwards. The sucking disc of the prehensile 

 antennse of the larva, in the five species examined, was a 

 little pointed, and in shape resembled the hinder hoof 

 of a mule : this may perhaps be accounted for by the 



