12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



Elizabeth Bay, Albemarle Island, Galapagos. The larger specimen 

 measures : Length, 8.6 mm. ; greater diameter, 10.7 mm. ; lesser 

 diameter, 9.2 mm. 



This species is related to Tegula (Chlorostoma) snodgrassi Pilsbry 

 and Vanatta, which comes from Albemarle Island. It is, however, 

 more depressed and of darker color with fewer light zones. 



It is named for Capt. G. N. Barker, of the U.S.S. Houston. 



PHLYCTIDERMA, n. subgen. 



Shell similar to Entodesma but anteriorly more narrow, with the 

 anterior half of the ventral margin more sinuous, and with surface 

 sculptured with very fine, radially arranged, white pustules which 

 become obsolete toward the margins. 



Type. — Lyonsia (Phlyctidenna) lucasana, new species. 



LYONSIA (PHLYCTIDERMA) LUCASANA, n. sp. 



Plate 4, figs. 1-3 



Shell of medium size, elongate, inflated, ventrally gaping, ante- 

 riorly subrectangular, posteriorly broader and more rounded. The 

 anterior end is inflated and blunt, the area anterior to and below the 

 umbones being somewhat concave. The umbones are rather promi- 

 nent and almost terminal, and the anterior end from the umbones 

 to the anterior ventral angle is about straight. The ventral margin is 

 strongly sinuous anteriorly. The surface is white, covered with a thin 

 pale brown periostracum arranged anteriorly in irregular vertical 

 stripes coalescing posteriorly into a more solid patch ; the whole sur- 

 face is covered with radially arranged fine white tubercles evanescent 

 toward the margins. The grosser sculpture consists of rounded con- 

 centric ridges crossed posteriorly by a few distant, low radial ridges 

 occasionally bifurcating; toward the posterior and ventral margin the 

 sculpture becomes rather irregular. Interior pearly, with an oval 

 anterior muscle scar and a bipartite posterior muscle scar, the lower 

 part being larger and suborbicular. Hinge teeth lacking ; a narrow 

 shelf for the ligament is present just below the dorsal edge posterior 

 to the umbones. 



The type, U.S.N.M. no. 472526, a single left valve, measures: 

 Height, 9.9 mm.; length, 18.5 mm. It was dredged in 6-10 fathoms 

 off Punta Gorda, Cape San Lucas, Lower California, Mexico. 



This species seems closest in general appearance to Lyonsia (Ento- 



