THE NAUTILUS. 



TJnio Diazensis sp. nov. 



Shell small, oval, thin, bluutly or truncately pointed behind, and 

 biangulated there; rounded obliquely in front, the curve meeting 

 the dorsal line with a distinct angle. Epidermis reddish-brown, 

 lighter above on the first growth, finely and obscurely striate with 

 minute scales, more apparent near the base. Lines of growth dis- 

 tant, about two. Rays nearly obsolete, or, if present, seen faintly on 

 the anterior end, or on the first growth. Umbonal ridge well-de- 

 fined, rather narrow. Posterior slope rather broad and raised into 

 a keel. Dorsal line nearly straight. Umbos small, broad and not 

 raised. Beaks with a double series of granular undulations. Dor- 

 sal plate thin. Shell cavity rather deep and broad. Beak cavities 

 slight. Cardinal teeth very small and light, more or less com- 

 pressed. Lateral teeth very narrow, slim and nearly straight. 

 Anterior cicatrices distinct ; posterior confluent. Cardinal of right 

 valve single. Dorsal scars under the plate. Nacre salmon or cop- 

 pery. Width H inches, length ^, diameter ?. 



Habitat : Lake Diaz, Volusia Co., Florida. 



Remarks: In 1887 we gathered about 2,000 of these little thin 

 shells in Lake Diaz, no other Unio being found in that lake, except 

 U. amygdalum Lea. They were always in white sand, with clear 

 and rather shallow water, and nearly all of one size. Affinity, U. 

 fuscatus Lea, from which our shell differs in being smaller, less trans- 

 verse, more inflated, having a much higher umbonal ridge well 

 marked, while in U- fuscatus the ridge is nearly or quite obsolete. 

 From U. coruscus Gould the Diaz shell differs in having always thin 

 lateral teeth, a thin dorsum and smaller cardinals and a high keel, 

 and is always a thinner shell. It differs from U. fryanus B. H. 

 Wright in being much less polished, lighter, less solid, fewer rayed, 

 greater umbonal ridge and more attenuated in front. In a "Check 

 List of N. A. Uniouid?e," published in 1888, a species of Unio was 

 listed as " U. diasensis," but was never published, and therefore does 

 not preoccupy the similar name now given above. 



Note. Types of all the above species will be sent to the National 

 Museum and duplicates of the types to the Academy of Natural 

 Sciences of Philadelphia. 



ERRATA. In THE NAUTILUS, X, No. 12, page 136, first line, for 

 " triangular, clavate," read " triangular-clavate." Eighth line, for 

 " narrower," read "narrow." Page 137, ninth line above the bot- . 

 torn, for " groove in the," read " groove under the." 



