TRIBE MYTILACEA. 255 



/. 12./. 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. E. Indies. 1 



P. Alba. Sow.Z. P. 1835. Triangular, fan-shaped, with radiat- 

 ing narrow riblets which (especially anteriorly) are armed with a 

 lew rather long scales becoming nearly obsolete ventrally : dorsal 

 edge straight, anterior broad and rounded, ventral ventricose : 

 vertex rather hooked. 4J. . 5J. Honduras. 



P. Atropurpurea. aSW, 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 recuse 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. Afra. 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. 2|. . 6. Cape of G Hope. 



P. Semicostata. Conr. Joum. 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. 3k. 



P. Squamifera, 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. 5j. . 10J. Panama. 



P Tuberculosa. 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- 



1 The P. Vitrea. 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. 



