360 



obliquely suboval or subovate, longer or higher than wide, and narrowest 

 behind, entire, not channelled anteriorly as in Cerithrtwi ; outer lip sim- 

 ple, inner lip thickened and somewhat reflected or expanded at the base. 



Surface marked by narrow, but prominent and rather distant, varix- 

 like ribs, that cross the volutions transversely, and that are themselves 

 crossed by smaller and closer spiral ridges, the points of intersection 

 being minutely tuberculate. 



Protection Island, J. Richardson, 1873 : " a single and not very perfect 

 individual". Sucia Islands, J. Ptichardson, 1874: "six well preserved 

 examples." The largest of these specimens is a little more than sixteen 

 millimetres in length. Similar specimens were collected at the Sucia 

 Islands by Dr. Newcombe in 1894 and 1896, and at the Nanaimo River, 

 by Mr. Harvey, in August, 1901. In the figure on Plate 15 of the second 

 part of this volume the number of volutions is represented as eight, but 

 the apical ones are slightly restored. The characters of the aperture are 

 well shewn in the specimen represented by figure 7 on Plate 44. 



The reference of the specimens collected by Mr. Richardson to the 

 genus Mesostoma (Deshayes, 1861) was first suggested by Dr. Stanton, in 

 1893, in his memoir on "The Colorado formation and its Invertebrate 

 Fauna," published as Bulletin No. 106 of the U. S. Geological Survey. 



Mesostoma (?) intermedium. (N. Sp.) 



Plate 43, fig. 4. 



Shell imperforate, elongate, slender ; volutions nine, those of the spire 

 obliquely flattened and very slightly convex ; the last volution moder- 

 ately inflated at about its midheight and narrowly rounded below ; 

 aperture higher than wide, subovate and abruptly pointed posteriorly ; 

 outer and inner parts of the lip unknown. 



Surface marked by numerou.%, narrow, rib-like folds, that cross the volu- 

 tions transversely, and by smaller and still more numerous spiral ridues. 



Sucia Islands, Dr. C. F. Newcombe, 1894 : four fairly good specimens 

 and one fragment. One of these is twenty-nine millimetres long and has 

 seven volutions preserved. Another was probably about forty millimetres 

 in length, when entire. Brennan Creek, V.I., Rev. G. W. Taylor, 1901 : 

 one good specimen and two fragments. The former is only seventeen mil- 

 limetres long, but has eight volutions well preserved, and there was pro- 

 bably one more at the apex. 



This species seems to differ from M. Suciense in its uniformly larger 

 .size, less ventricose volutions, and perhaps also in its soriiewhat finer and 



