— 30 —- 
nuato, incurvo ; umbonibus cordiformibus, area latissima ; dens 
cardinalis in valva sinistra duplex, in utraque erectus, crassus; 
margarita alba. 
Altit. 43. — Latit. 51. — Diam. 37. 
H. regiones superiores fluminis Usumasinta. 
81. U. CALAMITARUM. 
T. plano-convexa, forma pervariabilis, ovata, vel rhomboidea, 
nunc reniformis, arcuatim multistriata, castaneo-fuscescens, vel 
obscure fusca; latere antico brevi, rotundato; postico producto, va- 
riabilis ; dens cardinalis crassus, in valva dextra simplex, triangula- 
ris, in sinistra bipartitus; margarita alba, rosea, vel purpurascens. 
Altit. 29. — Latit. 51. — Diam. 16. 
H. rivulum Baluntié, prope Palenqueanum vicum. 
52. U. SCAMNATUS. 
T. ovata, convexo depressa, longitudinaliter tenuissime plicatula, 
castaneo-fulva, intus cerulescens; umbones depressi, strictim de- 
corticati; dens cardinalis in valva dextra simplex, triangularis, in 
utraque compressus. 
Altit. 30. — Lat. 55. —- Diam. 17. 
II. amnem Cacajajicara , in insula Cuba. 
83. U. PALUDOSUS. 
T. depressa, subcarinata, ovalis, olivacea, anterius rotundata, 
postice angusta, brevis; latere dorsali in alam triangularem medio- 
crem producto; umbones retusi, decorticati; dens cardinalis com- 
pressus, exilis; margarita roseo-violacescens. 
Altit. 31. — Lat. 57. — Diam. 15. 
H. paludosa prope S. Geronimo Yucataneorum. 
84. U. SCUTULATUS. 
T. depressa, ovata, tenuis, transversim striata, tuberculis sub- 
rhomboideis, planulatis, longitudinalibus, arcuatim plus minusve 
