THE NAUTILUS. 141 



fourth of the length ; hinge margin slightly curved, anterior end 

 narrowly rounded, posterior end much wider. Interior white, faintly 

 pink tinted in the cavity, hardly iridescent. Right valve with one 

 strong wedge-shaped cardinal tooth standing nearly at a right angle 

 to the larger axis of shell, slight rudiments of accessory teeth in front 

 of and behind it on the hinge-line ; the lateral single, stout and high, 

 separated by nearly its own length from the cardinal. Left valve 

 with two stout, subequal, oblique, crenulated cardinal teeth and two 

 strong laterals. Anterior adductor and pedal scars deep, posterior 

 scars very shallow, the adductor and foot retractor completely united. 

 Dorsal scars well within the cavity of the beaks, the major row (of 

 about 6-8 small deep scars) extending obliquely across the cavity 

 from below the cardinal to the lower side of the hinge-plate ; some 

 smaller, shallower scars below the main series. Pallial line deep an- 

 teriorly and below, shallow posteriorly. Length 111, height 71, 

 diam. 43 mm. 



Laguna de Atasta, near San Juan Bautista. Tabasco, Mexico. 



Type is a 9 specimen. It is allied to U. umbrosiis Lea, differing 

 in the narrower anterior end and consequently triangularly oblong 

 form, the hinge-line and basal margin converging strongly forward ; 

 the lateral teeth are also shorter. The female is much more swollen 

 posteriorly than in U. umbrosus. 



It is named in honor of Prof. Jose N. Rovirosa, known for his 

 botanical explorations in southern Mexico. 



This species falls into the genus Lampsilis as understood by Simp- 

 son. Pending the publication of his classification of the group, it is 

 here placed under Unio. 



SOME NOTES ON THE LAND SHELLS OF WESTERN FLOEIDA. 



BY C. W. JOHXSoX. 



The following notes on the land mollusca are based on a few ob- 

 tained incidentally while collecting fossils in Western Florida during 

 the latter half of February and the first week in March. 



These notes give a more southern and western distribution for a 

 nu miter of species than has heretofore been recorded. 



The more southern distribution is undoubtedly due to the direct 

 southerly course of all the rivers, which during freshets carry down 

 great quantities of drift-wood to which a number of the land shells 



