94 MONODONTA. 



markings upon the spaces between the blotches, while articulata is 

 all over closely lineolate in zigzag pattern, and the spiral series of 

 blotches are comparatively few and widely separated. Some speci- 

 mens are conspicuously spirally grooved, some are quite smooth. 



M. MUTABILIS Philippi. PI. 30, figs. 20-22 ; pi. 20, figs. 13, 14. 



Shell globose-conoid, umbilicate or subimperforate, solid resem- 

 bling a young M. articulata ; color usually grayish-yellow, yellow or 

 flesh-tinted, more or less obviously marked with obliquely radiating 

 lines or maculations of dull crimson, sometimes broken into tes- 

 sellations, sometimes faintly, minutely articulated with reddish, 

 appearing nearly unicolored ; spire short, conoid ; suture impressed ; 

 whorls 5 to 6, slightly convex, spirally finely grooved, the last some- 

 what flattened around the upper part ; aperture very oblique, large, 

 the lip forming half of a circle, not so much thickened nor beveled 

 within as in M. articulatus ; columella more flattened than that of 

 M. articulatus, scarcely edged with pearl, the tooth or lobe less 

 heavy, more acute than that species ; umbilical region always more 

 excavated than M. articulatus, the umbilicus open, or nearly closed 

 by the callous at the insertion of the columella. 



Alt. 16-18, diam. 17-19 mill. 



Mediterranean and Adriatic Seas- 



Trochus mutabilis PHILIPPI, Conchyl. Cab., p. 166, t. 26, f. 18-22 

 (1846). FISCHER, Coq. Viv., p. 314, t. 99, f. 2. BUCQ., DAUTZ. ET 

 DOLLFUS, Moll. Mar. du Rouss., p. 407, t. 49, f. 11-14. T. articu- 

 latus var. WEINKAUFF, Conchyl. des Mittelmeeres, ii, p. 355. 



A species which exhibits a curious combination of the characters 

 of M. articulatus and Gibbula richardi Payr. From the former it 

 differs in the finer sculpture, lighter columella and more excavated 

 umbilical tract; in the last character mutabilis approaches Gibbula 

 richardi. The dentition of the latter species should be examined ; 

 that of mutabilis, if correctly figured by Troschel (Des Gebiss der 

 Schnecken, ii, t. 22, f. 14), is similar to the other species of Osilinus* 



M. CRASSA Montagu. PL 21, figs. 27-30. 



Shell imperforate, subperforate in the young, globose-conic, very 

 thick and solid, dull grayish, densely marked all over with very 

 numerous fine flexuous or zigzag anastomosing purplish-black lines ; 

 spire conic; whorls 6 to 7, convex, the apex usually eroded and 

 orange-colored ; last whorl flattened around the superior portion * 

 base eroded in front of the aperture ; aperture oblique ; columella 



