UNIO. 521 
are probably only vague generalizations of the places mentioned by Morelet. According’ 
to Fischer and Crosse‘, Bocourt has also found this species, but they do not say in what 
locality. 
U. delphinulus is easily recognizable among the Central-American forms by the 
well-developed conspicuous wing, in which the two valves are grown together, so that 
they cannot be separated without breaking, and the opening and closing of the shell is 
only possible by its elasticity. This is the character of the artificial genus Symphynota,. 
Lea, and it is also the case in a Malayan species, Unio delphinus, Gruner. The 
nearest allies to U. delphinulus are, however, I think, the North-American U. inflatus, 
Lea, and U. alatus, Say, of the subgenus Metaptera, Raf. ; these agree with U. del- 
phinulus in the form of the wing, as well as in that of the whole shell, especially of 
its hinder end, and in the general coloration, but the teeth are comparatively somewhat 
stronger in the North-American forms. 
Dubious or insufficiently known Species. 
Unio largillierti. 
Unio largillierti, Philippi, Zeitschr. f. Malak. iv. p. 94 (1847) °. 
Hab. Yucatan (Largilliert 1). 
This species seems not to have been found again—that is, if it is really different 
from U. paludosus, Morel.*. 
Unio tamaulipanus. | 
Unio tamaulipanus, Conrad, Proc. Acad. Phil. vii. p. 256 (1855) *; Lea, Synops. Fam. Unionidz, 
p. 65 (1870) *. 
Unio tamaulipasensis, Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. p. 621°. 
Hab. N.E. Mexico: Rio San Juan, State of Tamaulipas (Conrad '~*). 
Insufficiently described, no measurements or figure given; it is said to be near 
U. niger, Raf. (incrassatus, Lea). 
* According to Philippi’s description (it is not figured), there are in the posterior part two furrows. 
descending from the summits, while in U. paludosus, according to Fischer and Cosse, there is a descending 
keel, oblique and obtuse: these definitions may have the same meaning, Philippi’s furrows being the 
depressions which border the obtuse elevated line. Further, the last-mentioned author says that the wing is 
rectangular, forming a right angle above (superius): if he means that the upper edge forms a right angle with 
the hinder edge, this may apply somewhat approximately also to U. paludosus. Moreover, he mentions a 
small true cardinal tooth behind the anterior lamellar ones, and the same is stated also by Fischer and Crosse. 
It is to be regretted that Philippi gave no measurements, but as he says “ pernobilis species,” and compares 
it with Dipsas (Cristaria) plicata, we may presume that his shell was of rather large size ; on the other hand, 
he states that he had only a young specimen from Largilliert. , 
BIOL. CENTR.-AMER., Terr. and Fluviat. Mollusca, June 1900. 66 
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