408 Mr. W. H. Benson on Tanysiphon. 



The examination of the animal not only proved that it was 

 distinct as a genus from Novaculinay but that it must be sepa- 

 rated from the family of Solenidse and annexed to that of the 

 Myacidse. Its nearest relations in that group are probably 

 Glycimeris and Saxicava, the young of the latter being furnished 

 with cardinal teeth. Tanysiphon is found at extreme low- water, 

 by digging to a depth of six inches^ or even a foot, in the mud, 

 and occurs in a vertical position. Dr. Cantor states that it is 

 not abundant, and that it was obtainable by his people only in 

 February and March. 



I now proceed to describe the shell. 



Tanysiphon, Benson, nov. gen. 



Testa subinsequivalvis, insequilateralis, transverse oblonga, umbo- 

 nibus prominentibus obtusis, extremitatibus (postica maxima) hian- 

 tibus, margine superiori subarcuato, ventrali subrecto. Cicatrix 

 siphonalis elongata ^ longitudinis testae invadens. Valvse dextrae 

 dentes tres, 1 anterior angustus prominens intrans, 2 laminares 

 transversi, medianus prominens, posterior major obtusus ; valvse 

 sinistrae dentes duo, anterior bilobatus, posterior major. Ligamen- 

 tum duplex, externum parvum ellipticum, vix convexiusculum, inter- 

 num lineare foveam posteriorem occupans, demum laminam cardina- 

 ^lem perpendiculariter truncans. Epidermis tenuis. Area interior 

 testae nitida, non margaritacea. 



T, rivalis, Bens., n. s. PL XII. B. fig. 3. 



Testa tenui, transverse oblonga, antice breviori obtusa, postice lon- 

 giori, angustiori, extus tenuiter striata et irregulariter remote 

 rugosa, epidermide pallide cornea ; natibus decorticatis latis pro- 

 minentibus, umbonibus obtusis ; valvis male congruentibus, per 

 spatium breve cardinale et ventrale solum tactum exhibentibus ; 

 humero umbouali antico breviter compressiusculo ; area interiori 

 caerulescenti-alba. 



Lat. 21, alt. 11, crass. 9 mill. 



Habitat in rivo, prope urbem Calcutta Bengalensem. 



Some of the teeth are apt, in large specimens, to become 

 obsolete. 



The following account is extracted from Dr. Cantor's letter 

 accompanying his interesting drawing of the animal : — 



" The siphons closely resemble those organs in Mya truncata, 

 Linn., Woodward, p. 317. fig. 220. Both are united in a finely 

 annulated compressed scabbard nearly equalling the length of 

 the shell. A raphe or seam appears along the inferior margin 

 of the scabbard. The free extremity is surrounded by tentacula, 

 which are distant, and of unequal length. The orifices of the 

 siphons are papillular j that of the branchial siphon, the larger, is 



