17 



a good deal of variation, mostly of the large pustulose variety. 

 Some of the shells were larger than any I secured at Port 

 Jackson, and amongst them were certainly some representa- 

 tives of A. kimheri. Some forms of A. retrojectus are very 

 difficult to separate from that species, unless the specimens are 

 very perfect. 



In conclusicm. — Dr. Pilsbry, I.e., founded the sub-genus 

 Meturo'plax for the reception of this species, chiefly on the 

 character of the dorsal area, "dorsal area indistinctly 

 dijBFerentiated" ; while, in typical specimens, this may be true, 

 this feature is not constant, and makes one hesitate to adopt 

 his sub-generic name at this stage. 



AcANTHOCHiTON CORNUTUS, Torr and Ashby, and 

 A. EXiLis, Torr and Ashby. 



(Trans. Roy. Soc. S. Austr., vol. xxii., pp. 217-219, Oct., 1898.) 



Until last year A. cornutus was only known from the 

 unique type taken by the writer at Marino, in South Aus- 

 tralia; but on January 24, 1920, I took a second at Cape 

 Jervis. Messrs. Gatliff and Gabriel each lent me a very fine 

 specimen that they had identified as A. exilis. I noted that 

 they were con-specific with my type of A. cornutus, and, 

 later, compared them with the type of A. exilis which is in 

 Dr. Torr's collection, and found that A. exilis is simply the 

 juvenile form of cornutus. I find a note in my note-book, 

 made a couple of years back, that these two forms were very 

 close tO' one another. 



The largest. specimen of the series dredged by Dr. (now 

 Sir) Joseph Verco was selected as the type of exilis, and was 

 only 3 mm. long; all the specimens were much curled and 

 somewhat bleached, whereas the type of cornutus was over 

 10 mm. long and well preserved. 



There are slight differences between the two, but not 

 more than can be attributed to immaturity; the minute 

 curled exilis certainly looked very different from the fine 

 specimen of cornutus, but they are undoubtedly the same 

 species. As cornutus was described on an earlier page than 

 exilis, it has that priority, and A . exilis is a synonym thereof. 



In the addendum to our paper, I.e., reference is made 

 to apparent ''eyes" on the dorsal area of A. cornutus. It is 

 interesting to note that small black specks are visible in the 

 shells of the three recently discovered specimens, before 

 referred to ; but I have not yet been able to determine whether 

 they are true eyes, or some other sense organ. The deter- 

 mination of their true character must be left to future 

 investigation. 



