DONAX. 



Plate I. 



Genus DONAX, Linnaus. 



Testa trigono-ovuta vel ohlonga, plus 77iinus ctmeata, inter- 

 dimi Jlexiiosa, agidvalvis, plerumque valde inaquilate- 

 ralis, latere postico sapissime ahrupte truncato, inter- 

 dmn IcBvigata, plerumque radiatim linear i-sidcata. 

 Denies cardinales alterius valva duo, alteritts unicus, 

 snperne hijidus ; denies laterales duo vel unns, plus 

 minus remoti Ligamentmn exteruum, hreve, plerum- 

 qiie bipartitum, partim post umhones positum. Im- 

 pressio nmscularis pallii sinu magno. 

 Shell triangularly ovate or oblong, more or less Tvedge- 

 shaped, sometimes flexuous, equivalve, generally very 

 inequilateral, the posterior side being often veiy ab- 

 ruptly truncated, sometimes smooth, generally radi- 

 ately linearly grooved. Two cardinal teeth in one 

 valve, and one in the other, bifid at the upper part ; 

 two or one lateral teeth, more or less distant. Liga- 

 ment external, short, generally bipartite, partially 

 placed behind the umboes. Muscular impression of 

 the mantle with a large sinus. 

 There is scarcely any assemblage of bivalves so distinct 

 in generic character as those which have been associated, 

 without change, from the time of Linna;us, under the head 

 of Donax. They are distinguished by little variation either 

 in form, sculpture, or colouring. In form they are typi- 

 cally of a triangular wedge-shape, the anterior side being 

 long and rounded, the posterior very short and abruptly 

 truncated. In sculpture they are, with few exceptions, 

 either plain, or, more generally, radiately linearly grooved. 

 In colour they are mostly of a uniform fulvous or dull 

 grey, frequently, however, tinted with rays. They have 

 neither the variety of contour nor the spines and lamina;, 

 unless excepting the B. scortum, which characterize the 

 Venus and Cockle tribes, nor do they excite the attention 

 of connoisseurs by much variety or brilliancy of colour. 



Of the species contained in the following monograph, 

 from sixty to seventy in number, more than half have not 

 yet been figured. The conchologists who have paid most 

 attention to this genus in the present day, are M. Deshayes 

 and Ml'. Hanley ; a few species have also been described 

 by M. Philippi and Dr. Gray. The habitats of the I)o- 

 naces are in almost all temperate and tropical seas; so 

 miscellaneous indeed are they, that their geographical dis- 

 tribution presents no special features for observation. 



Species 1. (Pig. 1 and 3, Mus. Cuming.) 

 Donax scortdm. Don. testa trigono-ohlongd, gihbosi, 

 umhonihus angulato-approximatis, sulcentralihus, con- 

 centrice sulirregulariter dense latnellosd, striis subtiU- 

 bus radiantibus deciissatis, lamellis anticis erectis,Jini- 

 briatis, interstitus clathratis, posticis tenuioribus nu- 

 merosis, ad angulmn plus minus squamato-spinosis ; 

 sordide alba, intus violaced ; latere antico snbangidato, 

 lunula oblougd, postico acutissime anguhdo, latissitne 

 concavo-trimcato. 

 The hide Donax. Shell triangidarly oblong, gibbous, 

 umboes angularly approximated, nearly central ; con- 

 centrically somewhat irregularly densely lamellose, 

 decussated with radiatiug striae, anterior lamellae 

 erect, fimbriated, interstices latticed, posterior la- 

 mella; thinner and more numerous, more or less 

 squamately spinose on the angle ; dirty white, violet 

 in the interior ; anterior side slightly angled, witli an 

 oblong lunule, posterior very sharply angled, very 

 broadly concavely truncated. 

 LiNNJETJS, Syst. Nat. (12th edit.) p. 1126. 

 Testa juvenis. Donax pnbescens, Linnaeus. 

 Hab. Cape of Good Hope. 



There can be little doubt but that the Linnaean D. pn- 

 bescens, represented at Pig. 1, is the young of the well- 

 known adult D. scoiium, Pig. 3. 



Species 2. (Mus. Cuming.) 



Donax dentifeea. Dou. testa trigono-ovatd, latiusculd, 

 compressa, antice rotundatd, postice acute crenulatd et 

 plano-truncatd, area dense granulato-striatd, versus 

 marginem bidentiadatd ; sordid^ cinered vel fulves- 

 cente, radiatim tenui-sulcatd, liris posting crenulatis. 



The toothed Donax. Shell triangularly ovate, rather 

 broad, compressed, anteriorly rounded, posteriorly 

 shaqily angled and flatly truncated, with the area 

 densely crenulately striated, towards the margin 

 double-denticulated ; dull ash or fulvous, radiately 

 finely grooved, the posterior ridges crenulated. 



Hanley, Pro. Zoo!. Soc. 1843, p. 6. 



Hab. Panama. 



An extremely characteristic species, chiefly remarkable 



for two pau's of interlocking teeth at the ventral posterior 



end of the shell. 



September, 1854. 



