532 LEPADID.E. 



The external membrane over the whole animal, excepting 

 the horny disc which covers the rostral face of the peduncle, 

 is very thin and transparent ; it is periodically and often 

 moulted, as may be inferred from the many old lines of 

 junction round the edges of the horny disc : it is irregularly 

 and pretty thickly (but not so thickly as in fig. 7) studded 

 with star-headed, minute points, from ^^ths °f an mcn * n 

 diameter, composed of hard chitine, seated on a short foot- 

 stall, and this on a circular, yellowish, slightly thickened 

 disc of the general investing membrane, appearing like a 

 halo surrounding each little point. These points are directed 

 obliquely upwards. There are none on the horny disc, 

 though particularly numerous close to its margin. Their 

 state varies much : just after a moult, when newly formed, 

 the spines are regularly star-headed, with quite sharp rays, 

 from two to six in number, with some of them occasionally 

 bifid ; but these points or rays soon become blunted, 

 and ultimately half the star is worn away, so that the 

 appearance then presented is that of a crescent with a 

 few blunt points on its convex side. At each exuviation, 

 the thickened membrane of the orifice with its strong ex- 

 ternal spines (the condition of which also varies according 

 to the period elapsed since the last moult), and of course 

 the whole internal tunic of the sack, with its spines and hairs, 

 are all moulted, together with the external membrane and 

 the little star-shaped points. In most specimens a barely 

 distinguishable band or bar of yellowish, slightly thickened 

 membrane, runs from the points (a), at the lower end of 

 the orifice, for some way obliquely downwards ; and at the 

 lower end of this bar the weak adductor scutorum muscle 

 (having transverse striae) is attached. This bar is often 

 strengthened by a prominent external fold of membrane, 

 but yet it is so flexible, and as it is united only to the 

 lower end of the orifice, I can hardly believe that it can, 

 by means of the adductor muscle attached to its opposite 

 extremity, have much power in closing the orifice. I 

 believe that this muscle acts simply in narrowing the 

 whole animal, so as to favour its movement within the 

 cavity in which it is imbedded. Owing to this position of 

 the adductor muscle, and its consequent little power in 



