166 



Dentalium hexagonum. T. elongata, attenuata, ossea, arcu- 

 ata, hexagona, angulis obtusis, lateraliter compressis, interspatiis 

 inornatis ; peristomate sexangulari. Long. 55, diam. 4 millim. 

 Hab. Hong Kong, in shelly mud. 



Dentalium buccinulum. T. modica, lactea prope apicem 

 rubiginosa, admodum arcuatum, longitudinaliter sulcis ad 30 ara- 

 ta, versus aperturam evanescentibus, ubi lucida. Long. 30 mill, 

 diam. 3 millim. Hab. Kagosima. W. S. 



Most nearly allied to D. curtum, but is more deeply grooved. 



Dentalitbi intercalatum. T. parva, albida, acuta, rapide 

 ampliata, ad apicem sulcis primum sex deinde 12 aequalibus lon- 

 gitudinalibus sulcata. Long. 18, diam. 2-j- millim. Hab. China 

 Seas. W. S. 



Dentalium strigatum. T. bene arcuata, albido-rubescens, 

 sulcis amplis concavis longitudinaliter striatis ad 13 insculpta, dis- 

 sepimentis angustis, obtusis. Long. 18, diam. 3 millim. Hab. 

 False Bay, C. Good Hope. W. S. 



Dentalium porcatum. T. modica, cretacea ad apicem plus 

 minusve rubiginosa, bene arcuata, sulcis tenuibus longitud. 12 sen- 

 sim ad 20 auctis arata. Axis 20, diam. 2.5 millim. Hab. Hong 

 Kong Harbor. W. S. 



Dentalium clavatum. T. parva, clavata, polita, tenuis fere 

 hyalina admodum arcuata lateribus oblique undulatis, versus aper- 

 turam valde contracta. Long. 10, diam. 2 millim. Hab. Hong 

 Kong ; not uncommon. W. S. 



This would be regarded as a Ditrupa had not Mr. Stimpson 

 given a figure of the animal, which he assures us is a mollusk. It 

 resembles D. coarctatum Desh. 



Prof. Agassiz made a communication on reversed bi- 

 valve shells, and exhibited a specimen in the Unto liga- 

 mentinus^ (Lamarck.) 



In this genus, on the right side in the normal shell there is one 

 cardinal tooth and one long laminar tooth, and on the left two car- 

 dinal and two laminar teeth. Reversion of bivalve shells is quite 

 rare, and generally not easily observed except in those with un- 



