225 



as the same species, as is also T. acjitico^tdtd, McCoy (Memoirs 

 Austr. Mus., iv., part 5, 1902, p. 301). 



The late Mr. Dennant kindly compared our South Aus- 

 tralian shells with McCoy's fossil form from Victoria, and 

 he thought they were not identical, nor conspecific with T. 

 reticulata,, Ten. Woods. However, I think it is too closely 

 allied to be regarded as a distinct species, so it has been 

 placed as a variety of T . tuargaritarea, Lamarck. 



Among the many hundreds of valves and living speci- 

 mens dredged by me, only 1 has shown any marked departure 

 from the type of this variety. This was taken alive at 23 

 fathoms in St. Vincent Gulf, together with 2 others, which 

 quite conformed to the type. This unique individual exactly 

 resembled a half-grown specimen of the common T . inar(jari- 

 tacea, Lam., obtained from Tasmania. The only other aber- 

 rant from our form seen by me is a specimen taken by Mr. 

 Zietz, at Corny Point, Spencer Gulf. It has the spines of 

 T. margaritacea and the same number of ribs, but the shape 

 is more that of T. lamarckii, found in Port Jackson, only with 

 fewer ribs and fewer spines, and with an even longer and 

 more concave posterior border, in which last character it 

 departs greatly from our South Australian variety. The oc- 

 currence of these two marked aberrants among numerous 

 examples of the ordinary form indicates some other explana- 

 tion for our variety than either locality or depth of water 



Modiola penetecta, n. sp. PI. xxviii., Hgs. lo, 16, 17, 18. 



Shell small, thin, ovate, ventricose. Beaks apposed, in- 

 flated, oblique. Post-dorsal line nearly straight, 11 mm. ; 

 anterior-dorsal line, 2 mm. Ventral border anteriorly 

 slightly convex for 8 mm. ; then rather more convex, and 

 merging into the semicircular posterior end, which, with a 

 more open dorsal sweep, forms a faint rounded angle with 

 the post-dorsal line. A heart-shaped area, 10 mm. by 8 

 mm., on the united valves anteriorly is bare and glistening 

 and sculptured with very low lamellar accremental striae. 

 The rest of the shell is very closely invested with a felted 

 periostracum of short hairs, with short, blunt projections on 

 each side. Internal border simple. Horn-coloured, lighter on 

 the umbonal ridge. Internally chestnut-brown in front, and 

 with pinkish-brown concentric bands, most marked, in the 

 dorsal two-thirds, elsewhere a bluish-white. 



Length, 21 mm.; breadth, 13 mm.: thickness, 11 mm. 



It differs from M. austral is, Lamarck, in its shorter, 

 rounder, anterior end, its greater proportional breadth, and 

 its rounder posterior end. Its hairs are more numerous and 

 close-set, shorter, and ''elk-horn" in shape, instead of simple. 



H 



