40 THE VOYAGE OF H.M.S. CHALLENGER 



Cliiton striatus, Blainville, Diet, des Sci. Nat., 1825, vol. xxxvi. p. 551. 

 Cliitonellus striatus, Sowerby, Conch. Illust., 1841, p. 7, No. 85, fig. 62. 



„ „ Keeve, Conch. Syst., 1842, vol. ii. pi. exxxv. fig. 1 ; Conch. Icon., 1847, 



fig. 4 a, b. 



,, gunnii, Reeve, Conch. Icon., 1847, fig. 5. 



„ rostratus, Reeve, Conch. Icon., 1847, fig. 6. 



,, oculatus, Reeve, Conch. Icon., 1847, fig. 7 a, b (not of Quoy and Gaimard). 



Cryptoplax striata + gunnii + rost rata, Adams, Genera of Recent Mollusca, 1858, vol. i. p. 484. 



„ „ Angas, Proc. Zool. Soc. Lond., 1867, pp. 224, 225. 



Cliitonellas striatus, Smith, Report Zool. Collections H.M.S. "Alert," 1884, p. 84. 



Habitat. — Port Jackson, Sydney. 6 to 15 fathoms. 



This form is the best known of the group, but even it has suffered at the hands of 

 systematic couchologists. Keeve, as Angas and E. A. Smith have previously suggested, 

 has increased the synonymy of the species by three names, viz., Cryptoplax gunnii, 

 Cryptoplax rostratus, and Cryptoplax oculatus. E. A. Smith recognises in the first of 

 these a fairly well-marked variety of Cryptoplax striatus, which occurs in Tasmania and 

 South Australia. 



The figure in Sowerby's Genera, and which is copied in Reeve's Conch. Syst., is not at 

 all characteristic, as the three posterior valves are placed so far apart ; but Deshayes, in 

 the second edition of Lamarck's work, accepts it as representing this species. 



Although this species has been described and figured so often, it has, so far as I am 

 aware, hitherto escaped conchologists, that a series of " pores " exists, which have the same 

 position as those in Cryptoplax larvceformis. It is, however, easy to understand how this 

 has been the case : the number and size of the spines in the pores, in the latter species, 

 vary considerably. They arise from a very shallow depression, which appears under a 

 lens as a small roundish bare spot, but the white colour of the spines causes them to be 

 more conspicuous than they would otherwise be. In Cryptoplax striatus the white spines 

 very rarely occur, and when they do they are very small ; the bare shallow depressions 

 have much the same character as in the other species ; they are, however, often very hard to 

 detect, and even appear to be of irregular occurrence. In all the eight spirit specimens I 

 have examined, I find that the four anterior pores, and those between the first and second 

 valves, are universally present, and I could distinguish them between the second and 

 third, and third and fourth valves, in nearly all. The hinder pores are more difficult to 

 make out, and only in two cases could I satisfy myself of their occurrence between the 

 seventh and eighth valves. The main reason of their having been overlooked is due to 

 the fact that dried specimens alone have almost invariably been studied, and in these the 

 pores disappear, but very occasionally they can be traced when they are carefully looked 

 for. The presence of these pores breaks down a distinction which has been made between 

 pore-bearing and aporous forms. 



