GASTROPODA. l" :i:: 



up the development of ll<li<-toma and conclude that it was derived from Ophilda 

 further, that the lltli>;rfinn>i line terminated with itself and that Kuomphalus, which 

 it resemMe- in many respects, was not derived from it but directly from OphiUta. 

 The connection with Ophileta must determine the position of Helirotoma since 

 that tft>nu< is most certainly not a member of the Pleurotomnrii<l<r, while we are 

 fully satisfied of its affinities with typical Euomphaliiln . 



The Calciferons formation furnishes at least one unquestionable species of 

 llt'licntoniH, vi/..: II. perstrintn Hillings. There is a small species (less than one-half 

 an inch in diameter) in the Shakopee of Minnesota, that seems to differ very little 

 except in size from our //. ntnl>ilirn(a of the Stones River group. Other species of 

 the Stones River group are //. tenntsstensts Safford, //. declivis Safford, //. planulutn 

 var. robusta U. and S., //. plomibfoftfM Ulr., //. verticalis Ulr., and H. granosa Ulr. The 

 I'.lack Hiver group has //. plnnulata Salter, the type of the genus, and //. tnuricata, 

 H. -pinosa and //. larvata of the same author. From the Quebec group of Canada 

 Killings described five species (eucharis, gorgonia, misera, proserpina and tritonia) with 

 characters apparently in strict accordance with Helicoloma. Only //. marginata II r. 

 is known to us from strata of the Cincinnati period. H. naresi Etheridge, an Upper 

 Silurian shell, and the Devonian //. serotina of Nicholson, probably belong to some 

 other genus. 



HELICOTOMA PLANULATA Salter, and var. BOBUSTA, n. var. 



PLATE LXX1V. KI08. IS-J7. 



Betieotomn vlanulata SALTKK, 1859, Can. Org. Hem., Decade I,j>. 14. 



//. planulata is distinguished from nearly all other species of the genus by having from three to six 

 strong, simple or double, revolving lines on the outer side of the whorls. Beneath the marginal notch- 

 ridge the outer side Is more or less distinctly concave. The summit of the ridge may be on the same plane 

 In all the whorls, but, as a rule, on each It It a little lower than on the preceding turn. Within the ridge, 

 which ls sharply elevated and marked on Its outer side by an Impressed line, the depressed upper side of 

 the whorls is quite flat. The under side of the whorls may be regularly convex or an obscure angle may 

 form the boundary of the umbilicus. A full grown Individual has flve whorls. On plate LXXIV, flgs. 

 10 and 17, are two views of what we consider as a typical example of the species. 



Var. ROBUBTA, n. . 



I'LATK I.XMV. f I... IS. 



This variety Is founded on a single Imperfect specimen. It has revolving lines like //. plantiluin, 

 but differs In certain respect* too obviously to be referred U) that species without question. In the Oral 

 place Its whorls enlarge more rapidly both In hlht and width. The Inner whorls are missing, but we are 

 well satisfied that the specimen consisted originally of no more than four whorls. Next the concavity of 

 the upper pan of the outer side of the whorls Is scarcely notlceat.:. Kmally the lines of growth Croat 

 this side more obliquely. 



Cation and locality. The typical form of thl species, excepting a slngl. from an unde- 



termined Trenton horizon in Lincoln county. Missouri, Is only known from ti,.- Kiark KIV.T limestone at 

 Pau<|ueite rapids of the Ottawa river. In Canada. The type of our var. rofouta Is from th>- stones River 

 group in Jo DavlaM county, Illinois. 

 CWfcrt<M.-E. O. Ulrlch. 



