314 TEE PEA RL Y FRESH- WA TER MUSSELS— SIMPSON. vol. xviii. 



is not a natural one, and is made up of what are probably depauperate 

 Unios of different groups. Desbayes and Julien' state that the animal 

 of Monocondylwa {Pseudodon) tuniida, Morelet, is identical in character 

 with that of Unto and Anodonta. This is corroborated by Fischer,^ who 

 probably based his statement on that made by Deshayes and Julien. 



There seems to be a peculiar tendency on the part of many of the 

 Naiades of southern and southeastern Asia to develop aborted or 

 imperfect teeth. This is shown in Cristaria; in the groups of Unios 

 typified by U. hengalensis and U. senipei'vivens, and in Unio biasianus, 

 in which, as has been heretofore mentioned, the laterals are blurred, 

 much as in some of the North American Margaritanas. Many of these 

 Pseudodons seem by the form of the shell and its general apijearance to 

 be closely allied to certain groups of Unios; thus P. planulata^ Lea, 

 which has defective laterals and cardinals, is very near in form, texture 

 and nacre to Unio marginaUs, Lamarck. However, since so little is 

 known of the anatomy of these Oriental forms, it is perhaps best for the 

 present to let the genus stand. 



Genus LEGUMINAIA, Conrad.^ 



In 1865 Conrad applied the above generic name to the Monocondyla'a 

 mardinensis of Lea. In the following year Vest* gave the name Micro- 

 condylcea to AlasmodonUi honelli of Ferussac. From a study of the shells 

 I believe the two species, together with a few others in southwestern 

 Asia that seem to be nearly related, should be placed in one genus, and 

 in that case the name Microcondyhva, which has generally been applied 

 to Ferussac's species, must be placed in the synonymy. The shells, for 

 the most part, are elongated and compressed, smooth, with slightly cor- 

 rugated beaks, and have somewhat the appearance of Spathas. The 

 hinge is without laterals, and in place of the cardinals there is in each 

 valve a single, low, comj)ressed tubercle or hook. According to Drouet,^ 

 the branchial lamelhe of L. honelli are joined on the back; the internal 

 are not adherent to the abdominal sac; the external are united to the 

 mantle throughout their whole length ; and Clessin states^ that the man- 

 tle is open the whole length, and in this respect the animal is like that 

 of Unio. Nothing definite is known of the soft parts of the Asiatic 

 forms. Pseudanodonta, Bourguignat, is no doubt a synonym. 



Genus TETRAPLODON, Spix.^ 



The above name was applied by Spix to Unio pectitiatus, Wagner, 

 which is believed by Lea to be the eqnivalent of Castalia truncatus 

 of authors. The name Castalia commonly ai)plied to this genus can 



> Nouv. Arch. Mus. d'Hist. Nat. Paris, X (1874), p. 118. 



2 Man. de Couchyl., p. 1001. 



sAmer. Journ. Conch., I, p. 233, 1865. 



4Verh. n. Mitth. d. Sieben. Ver. f. Natur., 1866, p. 201. 



5 Bull. Soc. Philomathique, 7th Serie, VII, p. 1. 



6 Mai. Bliitt., XXII, p. 129. 



^Testacea Fluviatilia Braziliana, 1827, j). 32, pi. xxv, figs. 3, 4. 



