546 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



MONOSTYLA LUNARIS Ehrenberg. 



This supposedly cosmopolitan species is, strange to say, rare in the 

 Isthmian collections; a single specimen from a creek flowuig into 

 Camacho Reservoir (3) and two from Rio Grande Reservoir (5) is the 

 total number of observed specimens. This contrasts strongly with 

 the remarkable abundance of other species of the genus, as well as 

 of Lecane. 



MONOSTYLA VIRGA, new species. 



Plate 24, figs. 1-3. 



The body is ovate and strongly gibbous posteriorly. The anterior 

 margins are nearly coincident; the anterior sinus of the dorsal plate 

 is not quite as deep as that of the ventral, and at the bottom it has a 

 short straight line, while the ventral sinus is rounded; both have 

 their sides slightly convex; anterior spines are not present. The dor- 

 sal plate is oval and but little longer than broad; the anterior margin 

 is considerably narrower than that of the ventral plate. The outline 

 of the ventral plate is nearly the same as that of the dorsal; it is 

 shghtly narrower and somewhat angular posteriorly, with a conspic- 

 uous transverse fold. The lateral sulci are deep, as indicated by a 

 faint line in figure 3 ; the lorica is not tesselate. The posterior seg- 

 ment of the body is small and rounded; it projects but little beyond 

 the lorica. The coxal plates are small and obtusely triangular. The 

 first foot joint is pyriform, the second large and rounded. The toe is 

 long, parallel-sided, fairly stout and shghtly decurved; it has two 

 obscure annular constrictions. The claw is short and stout; it is 

 distinctly double, although the two parts are only rarely separated. 



Total length, 138 /i; length of lorica, 84 /i; width of anterior edge 

 of dorsal plate, 32 fx, of ventral plate, 42 n; length of dorsal plate, 

 78 }i, width, 72 pt; %vidth of ventral plate, 66 jul; length of toe without 

 claw, 48 /I, claw, 6 jx; depth of body, 45 //. 



Type. — Cat. No. 16584, U.S.N.M., from Rio Grande Reservoir (5), 

 where the species is abundant. The species occurs also in a pool 

 between Black Swamp and Gatun (2), few; pond at Bohio (7), few; 

 pond east of Empire (8), few; Rio Trinidad, above Agua Clara (10), 

 few; at Escoval (11), few. 



This species has considerable resemblance to Monostyla crenata and 

 was at first supposed to be a small variety of the latter; this, as it 

 proved later, erroneous assumption is the basis of the record in the 

 original description ^ of M. crenata as common in Isthmian collections. 

 The lateral view of M. virga shows at once that it is a different species. 

 In M. crenata the lorica is widely open in front, when the head is 

 completely retracted . 



1 Proc. U. P. Nat. Mus., vol. 46, 1913, p. 399. 



