162 THALESSA. 



Subgenus Thalessa, Fl. and A. Adams. 



P. RTPPorASTANEUM, Lam. PI. 45, figs. 42, 43, 36 to 41 ; PI. 46, 

 fig. 45. 



Yellowish or whitish, more or less motile*! or stained with 

 dark chocolate, which is sometimes disposed in hands between 

 the spinose revolving ribs; internally whitish with darker revolv- 

 ing bands. Sometimes the surface is nearly covered with black, 

 and a broad band margins the outer lip. Length, 1*5-3 inches. 



Philippines; Zanzibar; Paumotus ; Central Pacific ; 



Bay of Muscat ; Indian Ocean. 



The description of Linnaeus' /'. hippocastaneum is too indefi- 

 nite, and his references include other species; so that I am com- 

 pelled to cite Lamarck. 



P. bitiibervu laris , Lam. (fig. 36), is merely a black variety, in 

 which the outer lip is generally broadly margined with black ; it 

 has no distinctive characters in the tuberculation. 



A similar form from the Red Sea has been called P. ttamgnyi 

 (fig. 45) by Deshayes. 



P. distinguenda. Dunker < fig. 37), is a depauperate form of the 

 black variety, the whorls merely nodulous instead of spinose. In 

 P. intermedia, Kiener (fig. 41), even the nodules have almost 

 disappeared and are principally indicated by white spots upon 

 the otherwise dark surface; P. ocellata, Kiener (fig. 38), is the 

 young of this form. It may be convenient to designate P. inter- 

 media as a variety. Another variety is P. alveolata, Reeve, 

 which I have also figured (fig. 40). It is whitish or brownish, 

 the tubercles darker ; interior 3'ellowish, mottled with brown. 



Length, 1*25 inches. 



Panama. (Cumiug. ) Formosa ; Japan and Swan River. 



(E. A. Smith.) 



P. TUMULOSA, Reeve. PL 46, figs. 44, 48. 49 ; PL 45, figs. 33, 34 ; 



PL 47, fig. 65. 



Revolving ribs rounded, raised into round nodules superiorly ; 

 outer lip thin, not dentate within. Color varying from very 

 light brown to dark chocolate, more or less mottled with white, 

 especially the tubercles. Length, 1-2 inches. 



Zanzibar ? ; Japan. 



