NEW ANTILLEAN MOLLUSKS REHDER 193 



often knobbed at the edge of the sutural channel. On the early 

 whorls there are some axially directed rose spots, as in A. cruentata, 

 but on the later whorls these become straw brown and much reduced. 

 At the periphery is an acute keel, provided with large, regular, an- 

 teriorly hollow, triangular spines, which increase in size toward 

 the aperture, giving the shell much the appearance of an Astraea. 

 On the periphery, just below this keel, is a narrow spiral cord with 

 regular, small, low, anteriorly hollow scales, and below this is a 

 minutely serrate keel. The channels between these keels are sculp- 

 tured with fine axial threads. Below the last keel the flattened base 

 is sculptured with four low beaded cords. Two broad cords enter 

 the narrow, deep umbilicus. The slightly expanded circular aper- 

 ture is thicker externally; interior with a yellowish pearly luster. 

 The operculum is typical, multispiral, concave, the whorl:- orna- 

 mented with crowded, radially elongated, calcareous beads. 



The type, U.S.N.M. No. 536054, was collected on Sand Key, 8 miles 

 south of Key West, by G. W. Van Hyning. It measures : Height, 8.7 

 mm. ; breadth, 10.8 mm. 



This species is obviously related to Arene ouentata Mi'ihlfeld, but 

 has a different color pattern and the microscopic axial threads are 

 absent. The rugose axial sculpture on the upper surface of the whorls 

 is also less conspicuous and less regular. 



MICRODOCHUS, 2 new genus 



Shell very small, broadly ovate-conic; nuclear whorls smooth, post- 

 nuclear whorls convex, finely spirally Urate, somewhat appressed at 

 the suture to the preceding whorl with a consequently rather shallow 

 suture. Umbilicus narrow but distinct, aperture ovate, slightly 

 oblique, outer lip simple, columella!* portion slightly reflexed. 



Type : Microdochus florida?ius, new species. 



This genus of Rissoidae seems closest to Onoha Adams, 1852, dif- 

 fering markedly from it in being ovate conic and not cylindrical, m 

 having a shallower suture and a more open umbilicus, and in never 

 having axial riblets. 



MICRODOCHUS FLORIDANUS, new species 



Plate 20, Figure 6 



Shell very small, ovate-conic, rather thin, light horn colored. 

 Whorls 4*4, nuclear whorls smooth, not marked off from postnuclear 

 whorls, which are convex and finely and evenly spirally Urate, the 

 sculpture commencing imperceptibly; the whorls are slightly ap- 

 pressed to the preceding whorl at the suture, which is therefore not 



*iwcp6% minute + &o\6s, container. 



