492 MOLLUSCA. 
I. Crenoponta, Schliiter. 
1. Unio digitatus. 
Unio digitatus, Morelet, Test. Noviss. ii. p. 24 (1851) *; Fisch. & Crosse, Miss. Scient. Mex., Moll. 
ii. p. 563, t. 60. fig. 1°. 
Unio eightsii, Lea, Proc. Acad. Phil. 1860, p. 306°; Journ. Acad. Phil. (2) iv. p. 367, t. 64. fig. 192°; 
Obs. Gen. Unio, viii. p. 49, t. 14. fig. 192°. 
Near the following (U. stolli), but distinguished by a more four-sided, not circular outline, the posterior 
dorsal margin and the middle part of the ventral margin being nearly horizontal, and the radiating plaits 
increasing in size from above to below, the uppermost small, numerous, somewhat recurved forwards, 
the two undermost very broad and strong, running obliquely towards below and behind. 
a. Long. 180; alt. vert. 81, ale 86, diam. 46 millim. Vertices in } long. 
b 364, 114; . 75, , 82, 4, 47 4, ” t 9 
a. Dimensions taken from Fischer and Crosse’s figure ; 6, from Lea’s figure. 
Hab. 1N.E. Mexico: Rio Sabinas, Nuevo Leon (Eights 3-5). 
N. GUATEMALA: Rio Usumacinta, at deep spots (Morelet ! 2). 
The descriptions and figures of Fischer and Crosse? and Lea?4® evidently refer to 
one and the same species. But as regards the localities, it is scarcely credible that 
such a characteristic and large-sized Unio should live in two rivers so very far distant 
one from the other, and not have been found in the intermediate ones, as, for instance, 
in the Panuco or the Medellin. As to the locality given by Morelet}, there is no 
reason to doubt it, as he was himself in that country; but that given by Lea?4 5, 
‘Rio Sabinas,” may be a mistake for Rio de las Salinas, the name of the upper course 
of the Usumacinta. ‘There is, however, in N.E. Mexico, a town of Sabinas as well as a 
Rio Sabinas, on the confines of the States of Coahuila and Nuevo Leon, this river 
being a confluent of the Rio Salado, which discharges itself into the Rio Grande del 
Norte; there is also a Rio Salinas in the State of Nuevo Leon, a confluent of the 
Rio San Juan. I must therefore leave this difficulty for future elucidation. 
jj 
2. Unio stolli, n.n. (Tab. XXIX. fig. 2.) | 
Unio nicklianus, Kiister, in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Unio, p. 218, t. 73. fig. 3° 
(nec Lea); v. Mart. Sitzungsb. Ges. nat. Freunde Berlin, 1887, p. 107°. 
Testa subtrapezia, compressa, antice brevissime abrupta, postice alata, plicis crassis inequalibus a yertice 
retrorsum radiantibus sepius furcatis sculpta, superioribus in alam extensis, paululum antrorsum incurvatis, 
posterioribus magis validis, subhorizontalibus, inferioribus modicis, subverticalibus ; vertices compressi, 
margo dorsalis posterior primum in alam mediocrem ascendens, dein oblique stricte descendens; extremitas 
postica subrotundata, margo ventralis vix arcuatus, antice magis ascendens. Dentes cardinales validi, 
triangulares, sulcati. Facies interna alba, margaritacea. 
a. Long. 128; alt. vert. 62, ale 93, diam. 34 millim. Veertices in 1 long. 
& 6, 160; - , «x78, 4,128, , ? ,, - bo. 
a. Stoll’s specimen, type; 6. Kiister’s figure. 
Hab, N. GuateMata: Rio de las Salinas (Stoll 2). 
This species is intermediate between U. digitatus and U. nicklinianus: the plaits 
