GASTROPODA. ''''' 



LUMP! re Diiii*i ] 



resemble that speclea very closely (for comparison* nee preceding page) the affinities of L. progne are really 



much in-ari-r L. mirufa Hall sp. lnde<xl, the laat Is probably nothing more than a dwarfed variety of 



L. proynt, and If It r r tl> fact that It held IU own with remarkable constancy through a 



I and Is perbap* the most common type of the genus, we would be Inclined to place Its name 



on th>- li-t ? synonyms. The closed umbilicus distinguishes both very easily from L, amerioana, L. 



tirntciVi, and other species of the genus having an open umbilicus, while the extreme falntness of th<-ir 



suture lines and the flatneu or ull^ht conveilty of the upper surface of their volutions separates them 



e from such close allies of L. Helena Billings sp. and L. pertimilii Ulrlcb. 



Formation and tocoftty.-Stonea River group, Murfreesboro and Lebanon, Tennessee; Black River 

 and Trenton groups. If ercer count). Kentucky, and near Ottawa, Canada; Trenton group, Clltambonltes 

 and Fuslsplra beds, Ooodhue and Flllmore counties, Minnesota. 



CbOse(Mi.-B. O. Ulrlch. 



LlOSPIRA ANGUSTATA, fl. SO. 







PLATE LXVIII. FI08. IS-W: PLATE LXIX. FIOS. !-. 



group variety: Width about 17 or 18 mm., bight about mm.; apical angle 125. 

 Trenton group variety. Width 28 to 45 mm., hlght 15 to 22 mm.; apical angle about 130. Number of 

 volutions four to five. 



This speclea, cast* of which are exceedingly like those of L. amtritana and L. pngnt. Is distinguished 

 from the former by the great and gradually Increasing deposit of shell-matter on the umbilical side of the 

 whorls, and from the latter by the fact that this deposit does not, as Is the case In that species, Oil the 

 umbilical cavity entirely, but leaves a narrow subcentral perforation. As shown In figure 37 on plate 



1 II. the umbilical perforation Is relatively much larger In the younger stages of the shell than It Is 

 In fully grown examples, showing that the deposit, which we take to be a callous reflection of the Inner Up, 

 was proportionally much greater In later stages of growth. The callosity did not spread Itself over the 

 bottom of tli.- umbilicus but was confined to Its sides, and herein lies the principal difference between 

 /.. anytatata and L. proyne. Another difference Is that the anterior outline of the lower Up Is more broadly 

 and less uniformly convex. 



Formation and locality. -Of the small Stones River group variety we have four specimens which 

 one of us collected in the Vanuxemia bed at Minneapolis. Of the larger variety, which occurs In the 

 rusisplra bed of the Trenton group at several localities In Flllmore county, we have five specimens. 



CWfadtoMj. Geological and Natural History Survey of Minnesota; E. O. Ulrlch. 

 JTMeMiM Register, No. 74M. 



LlOSPIRA OBTU8A, tl. Sp. 

 PLATE LXVIII. riOS. -*. 



Hlght of a large specimen 26mm., width of same 44 mm.; blgbtof a small example 17 mm., width of 

 name 32 mm. Volution* four to five, with the periphery rounded and the upper side very slightly convex. 

 Umbilical cavity rather large In casts but In the shell Itself It Is Oiled, excepting a minute central 

 perforation, by a distinctly outlined, thick external deposit on the Inner side of the whorls. This deposit 

 is as heavy relatively on the Inner whorls as on the last. The last feature, together with the obtuse 

 character of the periphery, distinguishes this speclea from L. anyustata. 



Among a lot of Lower Silurian (ftutropoda kindly sent us by Prof. J. M. Safford, we flnd two speci- 

 mens which he collected from the " Ridley limestone" In Rutherford county, Tennessee, which agree in 

 all respects with this speclea save that the umbilicus Is not constricted by a deposit of shell such as we 

 flnd in this and the preceding species. The umbilicus i* about a* large as In L. rttnmo but the margin of 

 It, though rather abruptly rounded. Is not angular as in that species. We believe these speclsMM 

 represent another undescrlbed species of tin- Important genus and one that, If time and space had 



