32 THE VOYAGE OF H.M.S. CHALLENGER 



F. — Placiphoroidea. 

 Plaxiphora, Gray. 



Dall subdivides Gray's genus Plaxiphora {Placiphora, Carpenter and Dull) into three 

 subgenera in addition to the genus proper, viz. (a.) Fremblya, H. Adams ; (b.) Euplaci- 

 phora, Shuttleworth ; and (c.) Guildingia, Carp. They all agree with the genus 

 proper in having the insertion plates regular, ribbed behind ; numerous slits in the anterior 

 valve, one in the intermediate and none in the posterior valve, and small eaves. In 

 Plaxiphora the teeth are slightly propped ; there is a small sinus, and the sutural laminae 

 are joined ; swollen ribs ; girdle hairy, with regular pore-tufts. The type is Plaxi- 

 phora carmichaelis, Gray (= Plaxiphora setiger, King, from Patagonia). In Fremblya 

 the teeth are excurved, the sinus broad and shallow, girdle as above, the outbending of 

 the teeth being the distinctive character. The type is Fremblya collei, H. Adams, from 

 Australia. In Euplaciphora the teeth are sharp, the sinus broad, deep, and spongy, the 

 girdle with crowded hairs, but without pores. Type, Euplaciphora petholata, Sow., 

 from South Australia. In Guildingia the teeth are sharp, very long, and smooth ; the 

 sinus broad, deep, spongy ; the girdle encroaches on the valves, with pore-tufts and eniar- 

 ginate posteriorly. Type, Guildingia obtecta, Carp., from New Zealand, Mus. Cuming, 

 No. 45. 



As I have not the opportunity of critically examining these subgenera, I shall, for the 

 present at all events, refer all the three species collected by the Expedition to the genus 

 Plaxiphora. Carpenter admitted that a main distinction between this genus and Eupla- 

 ciphora lay in the absence of sutural tufts in the girdle of the latter, but he described in 

 his MS. Plaxiphora simplex, n. sp., as Euplaciphora, although, as is shown on Plate III. 

 fig. 13 b, sutural tufts are present; and in the type-species of Plaxiphora, Plaxiphora 

 carmichaelis, the numerous scattered tufts only imperfectly take on a sutural arrangement. 



The species of this genus are confined to the Southern Hemisphere. 



Plaxiphora carmichaelis (Gray) 



Chiton carmichaelis, Gray,',Spicilegia Zool., 1828, p. 6, and Wood, Index Test., Suppl., 1828, p. 1, 

 pl.'a fig. 10. 

 „ setiger, King, Zool. Journ., 1830-1831, vol. v. p. 338, and Sowerby, Conch. Illust., 1841, 

 No. 95, fig. 17. 

 fremblii, Broderip, Proc. Zool. Soc. Lond., 1832, p. 28, and Sowerby, Conch. Illust., 1841, No. 

 95, fig. 4. 

 „ biramosus (?), Quoy and Gaimard, Durville, Voy. "Astrolabe," Zool., 1834, vol. iii. p. 378; 



Atlas, pi. lxxiv. figs. 12-16. 

 „ setiger, Desbayes, Lamarck, Hist. Nat. Anim. s. vert., 1836, vol. vii. p. 513. 

 ., „ Reeve, Conch. Illust., 1842, vol. ii. p. 10, pi. exxxi. fig. 4, and Conch. Icon., 1847, pL ix. 



fig. 48a ; var. 13, fig. 48b ( = Plaxiphora fremblii). 



