172 TRANSACTIONS OF THE WAGNER FREE 



group in America would seem to be characteristic of the lower beds of the 

 Southern Miocene, as far as our present knowledge permits us to judge. 



I have observed that, occasionally, the ridge on the shoulder in young 

 specimens is represented by a nodule rather than a ridge. 



The essential difference between Ortliaulax and Hippochrenes, Calyptro- 

 plioms, Rimella, etc., is that the involution of the spire, once commenced, is 

 carried on by the posterior edge of the last or growing whorl continuously 

 from the young condition in Ortliaulax ; while in the others the spire remains 

 normal until the shell reaches its adult state and then, with the changes in the 

 mantle, which incite the deposition of the thickened and enlarged outer lip, 

 a process is developed at the posterior commissure of the aperture and man- 

 tle, which deposits enamel on the spire against which it lies, and it thus forms 

 a gutter, sometimes straight, sometimes recurved, in which it is sheltered ; 

 apart from this the spire is enveloped, if at all, not by any expansion of the 

 lip, but by a deposit of enamel which covers the whole, as frosting does a cake, 

 without any relation to the coil of the shell considered as an organic product. 

 Strip off the whole involving, continuous enamel from Calyptrophonis and the 

 whorls will remain intact; strip off the equivalent deposit in Ortliaulax s.nd 

 the shell itself is destroyed. The latter, so far as its structure is concerned, 

 is more nearly like an involute Terebellum (such as T. sopituin Brander, fig- 

 ured by Zittel) than like the enamelled Calyptrophorus or winged Hippochrenes. 



The latter wait until they have attained their majority and then spread 

 their outer lips and lay down their enamel, once for all. In Ortliaulax the 

 involution, as in (9e'2</z/?«, begins before maturity and continues with the growth 

 of the shell without regard to its age or periodical resting-stages. In this 

 particular it is clearly distinguished from any other group included in the 

 StrombidcB, excepting the sufficiently distinct Terebellinn. 



Subgenus Rimella Agassiz. 

 Rimella Smithii n. s. 

 Plate 10, figures 4, 6. 



Upper Eocene at Martin Station, Marion County, Florida, and at Rich- 

 ard's quarry, Ocala, Florida. 



Shell small, slender, subfusiform, with an acute spire and nine or ten gently 

 rounded, reticulated whorls ; each whorl has one prominent, thick, rounded 

 varix, over which the sculpture passes unchanged, but the adult shell termi- 

 nates in an elaborate sharp-edged lip and gutter as in ordinary Rimella ; spiral 

 sculpture of numerous regular, rounded, even threads, with subequal inter- 

 spaces covering the whole shell ; transverse sculpture, first, of the aforesaid 

 varices, which are not regularly spaced, but are found one on each whorl to 

 the very apex, representing resting-stages ; secondly, of numerous (on the 

 penultimate whorl about 30) rather sharp, elevated ridges, with wider inter- 

 spaces e.xtending clear across the whorls and overridden, without nodulation, 



