TRIBE MYTILACEA. 255 
t. 12. f.17. Narrow-subtriangular, dorsal edge much longer, sub- 
incurved, and angulated at the end, posterior ventral nearly straight; 
pellucid horn-coloured with about 10 broad, rounded, slightly scaly 
ribs : anterior base obliquely arcuated. 6. EH. Indies. } 
P. Atsa. Sow. Z. P. 1835. Triangular, fan-shaped, with radiat- 
ing narrow riblets which (especially anteriorly) are armed with a 
few rather long scales becoming nearly obsolete ventrally: dorsal 
edge straight, anterior broad and rounded, ventral ventricose: 
vertex rather hooked. 43..53. Honduras. 
P. Arropurpurea. Son, Tank. Cat. Elongated-triangular, black- 
ish purple, with a few distant radiating ribs which soon become 
obsolete, a few very thin paler convex broad scales towards the 
rather narrow anterior base, which is slightly retuse near the very 
elongated and somewhat incurved dorsal edge, and _ then slopes ob- 
liquely without forming an angle, to the convex posterior ventral 
margin. 6. Indian Seas ? 
P. Arra. Sow. Z. P. 1835. Lanceolate, horn-coloured, some- 
somewhat radiatingly painted with brown: with radiating subobso- 
lete riblets which are armed anteriorly with loose broadish scattered 
scales: dorsal and ventral edges equal, anterior short and some- 
what rounded. 24..6. Cape of G Hope. 
P. Semicostata. Conr. Journ. A.N.S. p. 245. t. 20. f. 11- 
Narrow cuneiform, dilated at the base, smooth; yellowish, green- 
ish and irridescent near the apex, basal margin straight, anterior side 
ribbed, posterior with concentric sulci, interstices of the ribs trans- 
versely striated. Sandwich Isles. 3%. 
P. Sevamirera, Sow. Z. P. 1885. Sublanceolate, horn- 
coloured, with a few radiating riblets, which are armed with rather 
large, broadish and somewhat distant, subreflected rounded and 
hyaline scales: dorsal edge straight, anterior and ventral rounded 
and continuous : ventral area wrinkled. 3..6. C. of G. Hope. 
P. Maura. Sow. Z. P. 1835. Oblong, tumid, blackish brown, 
with radiating small obtuse nearly obliterated ribs, which anterior~ 
ly support vaulted and subreflected scales which become smaller 
toward the ventral edge: dorsal edge straightish, anterior edge 
somewhat rounded, anterior ventral subventricose, posterior ven- 
tral sloping. 54..103. Panama. 
P Tusercutosa. Sow. Z. P. 1835. Subtriangular, broad, black 
ish brown, with the scales paler; with obsolete radiating ribs, 
armed with short foliaceous, anteriorly incurved, vaulted, tubercle- 
' The P. Virrea. of Chemnitz. f. 772.—Philippi. p. 75.—W. t. 
13. f. 16. copied in our figures is not improbably the young of this 
shell, or possibly of Turtons Papyracea which is assuredly distinct 
and possibly but a variety of the British Pectinata. 
