ELMINIUS SIMPLEX. 353 



4. Elminius simplex. PI. 12, fig. 3. 



Shell ribbed longitudinally, dirty white ; radii extremely 

 narrow, smooth-edged ; scutum having an adductor ridge. 



Bab. — New South Wales (Sydney and Twofold Bay) ; Van Diemen's Land ; 

 tidal rocks, often attached to other Cirripedes, and associated with Balanus 

 nigrescens, Tetraclita purpurascens, Catophragmus polymerus; Mus. Brit., Cuming, 

 Stutchbury, and Darwin. 



This species, of which I have seen specimens from the 

 above three localities, all exactly agreeing with each other, 

 is perhaps the Australian representative of U. plieatus, 

 which seems to be confined to New Zealand.* In all 

 essential points it comes so near that species, that I shall 

 make the greater part of my description comparative. 



General Appearance. — In external appearance there is considerable 

 difference from E. p/icatus, for E. simplex is generally of a regular 

 conical shape, of a dirty-white colour, with the surface well preserved, 

 having moderately wide, not very prominent longitudinal ribs. The 

 orifice is rather small and pentagonal. The radii are extremely narrow 

 or linear, with quite smooth edges ; the sutures, however, are always 

 very distinct, and in the upper part, the alee are generally rather widely 

 exposed, as viewed from the outside. The largest specimen which I 

 have seen was '7 of an inch in basal diameter. 



The opercular valves are closely similar to those of E. plieatus, but 

 the scutum is generally a little more elongated, and the articular furrow 

 not so deep : in accordance with this last fact, the articular ridge in the 

 tergum is not so prominent as in E. plieatus ; but we have seen that 

 these several characters are highly variable in E. plieatus. The slope 

 of the basal margin of the tergum towards the spur varies in the pre- 

 sent species, in a strictly analogous manner, as it does in Tetraclita 

 porosa. 



Structure of the Parietes and Radii. — The parietes are not so thick 

 as in E. plieatus ; internally they are tinted pale purple ; when broken 

 transversely, a row of microscopically minute orange-coloured dots 

 can generally be distinguished between the outer and inner laminae ; 

 and these evidently represent the orange-coloured layer in E. plieatus. 

 The sheath also exhibits a faint tinge of orange. The radii are very 



* I am bound to state that I have seen too specimens of E. plieatus marked 

 Sydney, and one marked Moreton Bay, but in both cases the collectors had 

 visited New Zealand, so that a wrong habitat by mistake might easily have got 

 attached to the specimens in question. 



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