TUGONI A. 



Plate I. 



Genus TUGONIA, Gray. 



Testa aquivalvis, valde ineequilateralis, plus minus globosa, 

 opaco-alba, soUdiuscula, radiatim temdlirata vel stri- 

 ata, liris ad aream anticam interdum deaiueiitihiis, 

 latere antico perampliter gibboso, postico brevissimo, 

 coarctato-7-osirato, hiante, orificio rotundo, marginibus 

 callosis. Car do processn parvo cochleariformi, septo 

 brevi perobliquo snstentato, in utruque valvu, ligameti- 

 tmn co7itineute, compositus. 



Shell equivalve, veiy inet[uilateral, more or less globose, 

 opake-white, rather solid, racliately finely ridged or 

 striated, ridges sometimes wanting on the anterior 

 area, anterior side very largely gibbous, posterior very 

 short, contractedly beaked, gaping, orifice round, with 

 the margins callous. Hinge composed of a small 

 spoon-shaped process, supported by a short very ob- 

 lique septum in each valve containing the ligament. 



The genus Tiigonia was founded by Dr. Gray for the 

 reception of a characteristic form of Anatina inhabiting 

 the west coast of Africa, originally described by Adanson, 

 in his ' Natural History of Senegal,' with the name Le 

 Tugmi. The shell is of a rather solid opake substance, 

 curiously gibbously globose, with the posterior extremity 

 contracted, where the siphonic sheath of the animal is 

 exserted, into a conspicuous subtubidarly-beaked orifice. 

 Adanson mistook it for the shell of a Pholas. Chemnitz, 

 who, as shown by his admirable fig\ires (Conch. Cab. vol. 

 vi. pi. 2. f. 13-16), possessed specimens, described it as 

 living in abundance near the mouth of the Niger, and named 

 it "The Guinea Mga anatina" The genus is, however, 

 rare in collections, and Mr. Cuming has obtained no pre- 

 cise infonnation of its habitat. The specimens in his collec- 

 tion given in the accompanying Plate, appear to represent 

 six species, varying in form anil convexity and in the details 

 of sculpture. Some are radiately ridged throughout ; in 

 some the radiating ridges abruptly terminate on the pos- 

 terior side at a line sloping from the umbo. Five of the 

 species are from AVest Africa, one from Ceylon. 



Species 1. (Pig. a, b, Mus. Cuming.) 



TuGONiA GuiNEENSis. Tug. testu globosa, gibbosissimd, 

 alba, radiatim tenuiliratd, liris striis concentricis sub- 

 obsolete fenestratis, striis anlicis versus marginem. evani- 

 dis, latere antico peramplo, postico abritple rostrato. 



The Guinea Tugonia. Shell globose, very gibbous, 

 white, radiately finely ridged, ridges somewhat obso- 

 letely latticed with eoueentric striae, anterior striie 

 fading towards the margin, anterior side veiy large, 

 posterior abruptly beaked. 



Le tugon, Adanson, Hist. Nat. Coq. du Senegal, pi. 19. f. 2. 

 Mya anatina, pars, Gmelin. 

 Mya anatina Guineensis, Chemnitz. 

 Anatina ylobnlosa, Lamarck. 

 Mya tugon, Deshayes. 



Hab. West coast of Africa. 



M. Deshayes proposed to adopt the Prench appellative 

 of Adanson for the name of this species, but such a com- 

 pound is unclassical. Chemnitz was the first to distin- 

 guish the shell specifically from those included by the 

 older writers under the general term of Mya anatina. 



Species 2. (Mus. Cuming.) 



Tugonia divaeicata. Tug. testa sabquadrato-muld, 

 Candida, radiatim niinutissinie lineari incisd, versus 

 marginem poslicum uilide divaricatim currugutd, latere 

 antico rotundato, postico late snbangnlato-rostrato. 



The divaricate Tugonia. Shell somewhat squarely 

 ovate, white, radiately very minutely linearly engraved, 

 towards the posterior margin prettily divaricately 

 wrinkled, anterior side rounded, posterior broadly 

 subangularly beaked. 



Ilab. Ceylon ; E. L. Layard. 



Of quite a distinct type from the AVest African species, 

 the shell being apparently smooth, but under the lens mi- 

 nutely radiately engraved, while towards the posterior anil 

 posterior-ventral margins it is sculptured with very cha- 

 racteristic divaricating wrinkles. 



Species .3. (Mus. Cuming.) 



Tugonia compressa. Tug. testa suborbiculari-ovatd, 

 versus marginem compressa, lulescente-albd, nndiqne 

 radiatim liratd, liris irregular ibus, striis concentricis 

 clathratis et teniie crenulatis, latere antico peramplo, 

 postico brevissimo, late rostrato. 



The compressed Tugonia. Shell suborbicularly ovate, 

 compressed towards the margin, yellowish-white, ra- 



Febniary, 1863. 



