34 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
CHITON AFFINIS, Jssel. 
Chiton affinis, Issel, Mal. Mar Rosso, p. 234; Pilsbry, Man. Conch. vol. xiv. p. 181. 
flab. Suez, mud-flats ; Suez Bay, among coral. 
This form appears to differ from C. olivaceus, Spengler [= C. siculus, 
Gray] in the following respects. The girdle scales are in C. affinis smaller 
and bear a few well-marked strise, while in the other species they have more 
numerous and fainter strize, not being smooth as is stated in the text-books. 
Further, the “ smooth triangle on the ridge of each valve,” seen in C. olivaceus, 
is replaced in C. affinis by an oblong region at the ridge. The riblets again 
in the last-named shell are more rounded and the valves are, more or less, 
punctate, between them; also the lateral areas have in the specimens 
examined only two or three ribs (in Savigny’s figure four). I have gone into 
this detail since the Rev. A. H. Cooke has* stated that the two forms are one 
species, and this view has been accepted by Mr. E. A. Smith f, the latter adding 
C. aereus, Rve., as another synonym, a view in which I cannot concur {. The 
matter has an importance beyond the mere specific identification, since both 
authors have utilized the supposed identity as a factor in their discussion as to 
what, if any, forms are common to the Mediterranean and the Red Sea. In 
my view the two are distinct, though allied, species. 
TONICIA SUEZENSIS (Reeve). 
Chiton suezensis, Reeve, Conch. Icon. fig. 134. 
Tonicia swezensis, Reeve; Pilsbry, Man. Conch. vol. xiv. p. 206. 
Hab. Suez, mud-flats, also among coral; Suez Bay, among coral; Suez 
Bay, among coral, Kal el Kebira shoal; Suez Bay, Etuleh shoal, 2 fath. : 
Khor Dongola, washed out of dredgings of weed and coral, Engineer Islet, 
3 fath.; Khor Dongola, washed out of nullipore dredged in 5 fath., Beacon 
Islet ; Suakim Harbour, coral reefs ; Sudan Coast, among coral, Mersa Ar- 
rikiya, 1 fath. 
ACANTHOPLEURA SPINIGERA, Sowerby. 
Chiton spiniyer, Sowerby, Mag. Nat. Hist., n. s. iv. p. 287, Suppl. pl. xvi. fig. 2. 
Acanthopleura spiniger, Sowerby ; Pilsbry, Man. Conch. vol. xiv. p. 221. 
Hab. Suez mud-flats ; Zanzibar, &e. 
A long series of this well-known form, which Mr. Crossland notes is “ the 
common high-tide Chiton, everywhere in Hast Africa, on the cliffs of coral- 
rag at Djibouti, Mombasa, Zanzibar, Wasin, &c. ; also on stones on the edge 
of reefs of the East Coast of Zanzibar.” It has a wide range of distribution, 
occurring in Australia, the Philippines, &c. (for details see Pilsbry, J. ¢.). 
* Ann. Nat. Hist. ser. 6, vol. xviii. p. 394. t Proc. Zool. Soc. 1891, p. 392. 
{ See for a note on this species, Proc. Malac. Soe. vol. ii. p. 195. 
