970 THE PALEONTOLOGY OF MINNESOTA. 



[Lophospira serrulata 



specimens precisely like his in that respect. Two other features, however, shown in 

 his illustrations are less easily reconciled with our specimens, and we confess that we 

 can do so only by assuming that his drawings are not entirely trustworthy. We are 

 loath to admit so much variation in at least one of the characters for we have found 

 it to be remarkably constant in all other species. We refer namely to the direction 

 of the lines of growth. These, we believe, do not bend sufficiently backward and 

 forward in Salter's figures. In justification of our view we would point out the 

 fact that his two figures (1 and 1*) are not exactly alike, so that it is not entirely 

 unwarranted to assume that neither agrees exactly with the specimen. Then he 

 represents the upper carina as nearer the suture than we have seen it, and farther 

 from the peripheral angle than it should be if his description is correct is saying 

 that the first and third keels are equally distant from the second. 



As to Murchisonia tricarinata Hall, under which name Prof. Whitfield (loc. cit.) 

 referred to young examples of both L. serrulata and L. helicteres, we have not the 

 slightest doubt that Hall's fig. 6c was taken from an imperfect testiferous example 

 of L. serrulata. This specimen, however, has four carinae and is evidently distinct 

 from the type represented by his figs. 6a and b. It was moreover only doubtfully 

 referred to tricarinata by Hall himself. The validity of the species tricarinata, 

 therefore, must be determined solely by the original description and type and not 

 by Hall's second specimen which we have said is clearly referable to L. serrulata 

 Salter. L. serrulata is the only species of the genus known to us having the flange- 

 like peripheral keel serrated on the edge like a circular saw.* It is an excellent 

 specific character, though unfortunately leaving no trace of its presence on casts of 

 the interior. Still, the beds in which the species occurs in that condition are of 

 such a nature that very often an excellent artificial cast of the exterior can be 

 prepared from the natural mold enclosing the interior cast. The species is readily 

 distinguished by other peculiarities, as may be seen by comparing it with other species 

 described in this report. Some difficulty will probably be experienced in making a 

 successful separation between it and the next species, L. helicteres, particularly 

 when internal casts only are available. For comparisons see under that species. 



Formation and locality. Stones River group, in the Vanuxeinia bed chiefly, at Minneapolis and 

 St. Paul, Minnesota, Mineral Point, Janesville, Bellville and Boloit, Wisconsin, and Dixon, Illinois. 

 Also In the Black River group (Upper Buff limestone) atBcloit, Wisconsin, and in central Tennessee 

 (Carter's Creek limestone). In Canada the species occurs at Panquette's rapids in the Ottawa river in 

 strata said to be of the age of the Black River group. 



Collections. Geological and Natural History Survey of Minnesota; E.O. Ulrich; Prof. J. M. Safford. 

 Museum Reainter, No. 7283. 



Prof. WhltBsld on two occasions cnMlit-, oilier species with such keels, the first lime In Ucol. of VVK, vol. iv. p. :;;(. 

 where he says It is occasionally or frequently met with In Ulurchixonia (Loph<>*iiii >i. //;.(, ;,.. ami M. Irimi-imitu; I he second 

 time in 1886, Hull. No. vlll, Amer. Mils. Nut. Hist., p. 311. when he suys il occur* in ".Many t iin- si.i'chncns [of /./,//. 

 especially of .'/. iniHrri " | /.. hicfncta.] We arc convinced that In both cases he refers to specimens of the form which we 

 identify with L. terrulata Salter, since among the numerous specimens of L. belictemi and L. bicincta studied by us we have 

 never observed even a semblance of sneh a keel. 



