U N I . 



Genus UN lO. Ret:. 



■J>sta Iii/ms marf/ari/ncca, (pqiiii-alrh, sapis-viui' ni,r-qi(ilnte- 

 rnlU, pphkrmhh- cvii-yjirna.iemper indnta ; U.jammitam 

 exteniinii ,• cnrilo variabilh, deidi/jiis antkii vd ceil- 

 iralihits ii< vtrdqne vahuln 1-3 instrudus, srrpnis etiam 

 lamellis lateralibus vi-l jmiicis pmterea mimiliis; im- 

 pressiones muscnlares d/KP, poxtica composita. 



iSlR-11 pearly within, equivdve, almost always inccimlateral, 

 constantly clotlied with a conspicuous ciuderuiis ; 

 liirament. external ; hinge variable, furnished with one 

 or f.vo central or anterior teeth in each valve, and 

 strengthened besides, for the most part, by lateral or 

 posterior lamellae; muscular sears two. the hinder 

 one composite. 

 Somewhat more than a hundred years have elapsed 



since LinuEnus first arranged shells in an artificial, yet 

 simple, methodical, and easily comprehensible manner. 



mcrly disgraced the Proceedings of the Zoological Society, 



and still appear in those of the Academy of Natural 



j Sciences of I'liiladelphia, the few characters there specified 



i would equally apply to a score of other shells. An ordi- 



1 nary Uiiio, devoid of any striking peculiarity of sculpture 



j or of contour, cannot possibly be determined without the 



I aid of a really good figure, or of a description so long and 



' careful that few modern naturalists have the ])atience to 



elaborate it. Say's earlier species (those in the American 



edition of Nicholson's Cyclopedia) are so ill defined that 



even his own countrymen difler as to what shells he wished 



1 to indicate. 



I It is, perhaps, to be regretted tiiat so extensive a genus 

 ' as Unio was not subdivided in the present work, and the 

 ! name restricted to such species only as are provided witii 

 lateral laraellse, but the broad Lamarckian divisions, 

 1 adopted in the earlier volumes of the ' Iconica,' compelled 

 I tlie author, despite of his gradually changed views of 



Since that period,' certain early-appreciated and natural ! natural groups, to preserve the outlines, at least, of his 

 oenen («nch as typical Mya) have not even tripled in the j original design. Almmodonta, with its two prunary and 

 number of known species, whdst the Uuiom-s, of which „o lateral i,,i\., Monocondyl^a, with merely one primary 

 two or three only were distinguished by the (^,reat Sys- | tooth and no lamelte, are easUy distinguishable from the 

 tematist are now known to us by hundreds. Indeed, ' typical U.mm. As io P.eudodcn, with its single rud.- 

 methin- like a thousand so-called species have already mentary compressed tubercle in each valve, it had, perhaps, 



better have been wholly relegated to Anodon. Ingunoiloi, 

 and Phgioduu, each based upon one shell only, are of less 

 present importance. 



been described, and every year that indefatigable veteran, 

 Isaac Lea (the loving patron of the Naiades), adds bewd- 

 dering varieties, forms, or species (it is doubted which) 

 to the conglomerated aggregate. It is more than probable 

 that not one-half of the presumed species of ovir North 

 American cousins will stand the crucial test of eritieism ; 

 yet many of their really distinct forms have been here 

 unavoidably omitted, from want of specimens for delinea- 

 tion. Scarcely any of the shell-collectors of England care 

 for such sombre-hued objects ; hence the omnivorous 

 cabinets of Taylor, Hanley, and the British Museum, are 

 almost our sole sources of study. 



Independently of the remarkable diversity of outline 

 the male and female of each species (ditt'erences 

 far as we know, are comparatively imperceptibh 

 other genera), priority of nomenclature involves a never- 

 ending investigation ; for Conrad and Lea (both natu- 

 ralists of eminent ability) for the most part claim prece- 

 dence of eacli other on no common ground for arl)itration : 

 the former more usually from prior publication in |)rint 

 tlie latter from prior readings at some scientific meeting 

 As to sucli brii I' and utterly iiuidequalr diagnoses as for 



October, ISOS 



The United States of North Am 

 great bulk of the recorded species 



ca now furnish the 



South Auieriea, if 



ever investigated with equal energy, will probably yield 



us as many distinctive forms. Asia (China has, perliaps, 



to be excepted) seems comparatively poor, since British 



j India, although its conehologieal fauna has been fairly 



■ worke'd out by such enthusiastic naturalists as Theobald, 



Benson, and the Blandfords, scarcely adds more than a 



i score to our list. Europe, Africa, and Australasia (the 



' two latter, possibly, from want of exploration) are alike 



h, so 1 sparingly provided with Naiades. 



most 



Species 1. (Mus. Cuming.) 

 o BOYKINIANUS. Un. tentd mafjis iiiiviisn' rrassu, 

 1,1 medio veiilricosa, valde uMijiiituUrali, uhuialo-sub-^ 

 tri,iond,antici perbrevi angustatd el rolundald, poslice 

 lata depressd et alatd, olivaceo-nigresci 

 plicis vudtis obliquis saljamwtis aut Jl,. 



oneolore, 

 (d srrjie 



