L U C I N A 



Geuus LUC!INA, Bniguure. 



Testa 2dermnque orhicularis, aid plana ant g'Mosa, sapimme 



aquivalvis et inceqidlateralis, wmioniius parvis. Cardo 



variabilk, modo varie dentatus, modo edentattcs. Im- 



pressiones muscidares dktatdes, antica varie prolongata. 



Shell mostly orbicular, either flattened or gibbous, most 



frequeutly etjuivalve and inec|uilateral, with the 



umboes small. Hinge variable, sometimes variously 



toothed, sometimes toothless. Muscidar impressions 



distant, the anterior one variously prolonged. 



The species referred to the genus Lnchia in the following 



monograph, are a somewhat heterogeneous assemblage, 



comprehending ten or a dozen distinct types of form, 



each of which is characterized by a particular kind of hinge 



and external sculpture. Some of these forms have been 



regarded, and not improperly so, as separate genera, but 



all are alike distinguished in the interior of the shell by a 



prolongation of the anterior muscular sear. There are, 



moreover, few in which the internal surface of each valve 



is not peculiarly grooved, or striated, or punctured. 



These sections of the genus are severally represented by 

 the following species — L. tigerma, Jamaicensis, Fenmyl- 

 va/iica, Philippiana, borealk, deut'ifera, ChUdreni, 7;<'(?to;, 

 divarieata, cornea, and rotundata ; and the structure of the 

 hinge is regarded in each as a specific, not a generic 

 character. The shell varies exceedingly in composition, 

 being in some species extremely thin and fragQe, whilst 

 in others it is very stout ; it is, however, somewhat re- 

 markable for the absence of external colour or painting. 



In the first type, L. tigerma (Genus CodaJda, Scopoli), 

 the shell is characterized by an elaborate decussated 

 sculptm-e, and the valves are mostly red-coloured about 

 the interior margin; L. Jamaicensis represents a group 

 (Genus Phacoides, De BlainviUe) in which the shell is 

 only concentrically sculptured, and alhed to this in form 

 are the groups typified by L. Penmyhauica and denlifera, 

 the former being distinguished in form and by a pecidiar 

 horny epidermal coat, the latter by having the concentric 

 ridges serrated and sealed. In L. Cldldreni the shell is 

 remarkably inequivalve ; in L. pecteii and its congeners 

 it is variously radiately sculptured ; and in L. divarieata 

 and allied species (Genus Strigella, Tiu'ton), the external 

 surface of the valves is variously rippled, so to speak, 

 with waved divaricating lines. The shell of L. boreal is 

 (Genus Triodoiiia, Schumacher) is of a rounded solid 



August 



growth, very closely concentrically sculptui-ed. In all these 

 the hinge approximates more or less to the Femes type, 

 with sometimes the addition of remote lateral teeth, 

 though in one or two species all teeth are obsolete ; but 

 in the very characteristic group typified by L. PldUppiana , 

 most generically distinct of all, the shell is very gibbous, 

 thin, and always toothless, the hinge being strengthened, 

 in the absence of teeth, by a dift'erent position of the 

 ligament, which forms a broad strap, as it were, across the 

 dorsal margins of the valves. The hinge of L. rotundata 

 and several other species (Genus Biplodonta, Broun) is 

 remarkable for an erect bifid tooth, and iu L. cornea and 

 its allies, also very generically distinct, the shell differs 

 fi'om all the preceding types in being smooth with a polished 

 horny epidermis of a dai-k olive colour. The lunde of 

 the shell in most of these groups is curious, iu belonging 

 more to one valve than to the other. The shell, instead 

 of opening through the centre of the lunule, as in Artemis, 

 opens mostly on one side of the lumde. 



Of seventy Lucince here described, the localities are 

 known of about fifty. Ten species inhabit the seas of 

 Europe, ten are fi'om the Philippine Islands, L. horealis 

 being found iu both these localities, eight inhabit the West 

 Indies, seven the west coast of Central America, and the 

 remainder are from the Bay of Honduras, North Australia, 

 New Zealand, Eed Sea, Senegal, Brazil, Panama, China, anil 

 Peru. In noticing the geographical distribution of the 

 genus, the chief circumstances to be remarked are, firstly, that 

 the beautiful type represented in the Bay of Honduras by 

 L. tigerina and exasperata, appears at Torres Straits, North 

 Australia, in L. interrnpta, and at Panama in L. pimdala ; 

 and, secondly, that the characteristic form L. Pemmjhanka 

 from Jamaica, is represented at Senegal, on the west coast 

 of North Africa, by L. colimihella, and on the opposite 

 side of the continent, on the shores of the Bed Sea, by 

 L. speciosa. The European species have little or no 

 typical relation, and none of the types of the genus 

 appear to have any particular local character. 



Species 1. (Mus. Cuming.) 



LuciNA KUGIFEKA. Luc. iestd ovatd, longioru iiuam alia, 

 compressiusculd, radiatim subobscure sulcata, liris con- 

 centricis corrugati-s vndique compicue exscnlptd, sukis 

 radiantibus ad latera subprofmidis ; lucted, pallide 

 Sjiadiceo conceidrice fasciatd. 



1S50. 



