192 F. Haas: Beiträge zu einer Monographie der asiatischen Unioniden. 
Arcidopsis footei 'THEOBALD. 
(Taf. 15—16, Fig. 9). 
Haas, Conch. Cab., 1912, S. 112, Taf. 14, Fig, 3—4, — Sınmpson, Descer. Catal., 1914, S. 1191. — Preston, Freshw. 
Gastr. & Pelecyp., in Fauna Brit. India, 1915, S, 196. — PrAsHAD, Rec. Ind. Mus., Calcutta, XIX, 1920, 
S. 165, Textüg. 1. 
Die von mir (Conch. Cab., Taf. 14, Fig. 2) unter diesem Namen abgebildete Muschel schien 
mir immer schon verdächtig, weshalb ich (a. a. O., S. 121) auf ihre Ähnlichkeit mit einigen 
Trapezoideus-Arten hinwies. Mein Argwohn war nicht unbegründet, wie des Näheren bei Be- 
sprechung von Trapezoideus prashadi erwähnt werden wird. 
THEOBALD's Typus seines Unio footei scheint verloren gegangen zu sein und Beschreibung, 
sowie Abbildung seiner Art sind zu dürftig, um sich ein Urteil über diese bilden zu können. Es 
ist deshalb freudig zu begrüßen, daß PrAsuAaD im Indian Museum zu Calcutta Exemplare einer 
Muschel gefunden hat, die zu footei gerechnet werden müssen und die gestatten, eine aus- 
reichende Beschreibung dieser Art zu geben; das größte der erwähnten Stücke, von dem mir 
mein Freund PrasHaD eine Photographie verschaffte, ist hier auf Taf. 15-16, Fig. 9, abgebildet. 
Der Einfachheit halber wiederhole ich die von PrasnaD gegebene erweiterte Artdiagnose: 
Shell moderately large and thick; elongate, subrhomboidal, very inequilateral. The dorsal 
and ventral outlines are nearly straight and parallel in the young, but owing to an antero-down- 
ward slope of the dorsal side become greatly inclined in the adult, thereby greatly reducing the 
length of the anterior margin. Anterior margin strongly truncated above, rounded below; poste- 
rior margin truncated above and also truncated below in the young, but evenly rounded in the 
adult. A. small but distinct posterior wing, better marked in the young than in the full-grown 
specimens. Umbonal region prominent, sligthly swollen and opposed in the young, becoming 
depressed and less marked in older specimens; sculptured with numerous low corrugated ridges 
arising from an excentrically situated nucleus, and radiating outwards on the two sides but 
more or less parallel in the middle region; a few very minute striae also run transversally in 
this region. Older specimens with the beak much eroded and bleached and showing barely any 
striations, Shell swollen in the middle but depressed in front, below and behind, Periostracum 
coarse, with strong vertical ridges in the young radiating outwards, some with a very marked 
V-shaped course, In adult shells the striations less marked but distinct; a few minute transverse 
concentric ridges also visible in both young and adults; regions of growth well marked. Perio- 
stracum of a yellowish brown colour with a few light green striae along the vertical striae, 
specially distinct in the young specimens. Nacre pearly white, iridescent. Hinge strongly deve- 
loped; pseudocardinals three in the right valve with a middle tooth best developed, two in the 
left, the outer being much the larger; all these teeth vertically striate in adult shells. Laterals 
lamellar, nearly straight, one in the right, two in the left valve, in which the lower ridge is better 
developed, being longer and stouter than the upper. Muscular scars. moderately impressed; an- 
terior scars confluent, posterior scars distinct. Pallial line distinct though not deeply marked. 
Measurements of shells (in millimetres) 
Length 17,1, breadth 10,2, height 7 mm. 
ir 25,2, " 1585,00 89, 
u 43,4, Mr 232, „ 7,1 „ (Single left valve!). 
