NO. 1152. CAMBRIAN BRACHIOPODA—WALCOrT. 391 



is shown in the former illustrations of that species, and we now have 

 good material of L. davisi, the type of LingiUella, and of several closely 

 allied species. Before making any comparisons I wish to call attention 

 to the observations that have been made by Salter, Davidson, and 

 Mickwitz. In the original description, Salter calls attention to the 

 r(iscniblaiicc of the inuscnlar scars of Lingulella to those of Oholiis, 

 but he considers that the difference in relative position is sufficient to 

 distinguish the two genera. Attention is also called to Oholella Bill- 

 ings, and to the fact that the later figures of Billings "show a very 

 (1 liferent set of muscular scars."' Davidson had the same material 

 that Salter had and more, but was unable to find any satisfactory 

 interiors, and hence left the genus as doubtful; but he evidently 

 considered it as nearly related to Liugula. 



Mickwitz met with the same difficulty as Davidson, in having unsat- 

 isfactory material upon which to base an opinion. After stating that 

 Oholrllti liillings would i)robably have to make room for the genus 

 Obolus Eichwald, he says: 



Whether imf/M?eHa Salter will share the same fate, I will not ventiiie t() preilict 

 with tli<^ same dejijree of certainty, since tlie diagnosis and tignres are even more 

 imperfect than in Billings's genns.- 



Atfirstthought American paleontologists will be inclined to consider 

 that there must be strong generic distinctions between Oholus and I/ingu- 

 lella. They have been accustomed to think of Obolnn as a thick, strong 

 shell, possessing such prominent and peculiar interior scars and mark- 

 ings that nothing in Li)u/uleJla would suggest generic identity. If we 

 consider, however, that Obolus occurs in the Cambrian and Lower 

 Ordovician strata of continental Europe, and that it has not been 

 unquestionably recognized in America at the same horizons, we are 

 led at once to ask, What represents it in America? The first answer 

 is, OboleUa; but when we compare the calcareous shell of Obolella with 

 the semiphosidiatic shell of Obolus, and note the marked difference in 

 the interior of the ventral valve as compared with that of Obolus, we 

 can hardly share Mickwitz's view that the two are congeneric, or, at 

 the best, that Obolella is a subgenus of Obolus. If Obolella, does not 

 represent Obolus in America, there is only the widely distributed 

 Lingulella to compare with Obolus. 



The study of a series of finely preserved specimens of Obolus celatus 

 Volborth leads to the conclusion that the small, thin shells of the 0. 

 celatus type are representatives of the Lingulella type in America and 

 Britain. If the comparison is extended to Obolus apollinis^ it is found 

 that it is essentially the same, except that the muscular and other 

 markings have been more strongly impressed on the thicker shell. In 

 order to facilitate a comparison of Obolus and Lingulella, figures of the 

 interior of the shell, drawn from specimens of Obolus celatus and 0. 



I Mem. Geo]. Surv. Gt. Brit., 1866, III, p. 333. 



'^M^-m. Acad. Imp. St. Pctershourg, 1896, 8th scr., IV, No. 2, p. 126. 



