154 Trans. Acad. Sci. of St. Louis. 



to comprehend the motives for this association. In Surcu- 

 loma the beak is rather slender and somewhat abruptly formed 

 below the convexity of the body whorl, the ribs large and few 

 in number, the spire whorls always more or less angulate in 

 profile at the periphery and the sculpture invariably consists 

 of minute and very close-set spiral lines. In Amblyacrum, 

 however, the beak is thick and gradually formed, the ribs 

 numerous and close-set, the spire whorls almost evenly arcuate 

 in profile and the spiral sculpture coarse and not close-set. 

 The general f acies of the shell in the two genera is wholly differ- 

 ent. There are four species of Surculoma known to me at pres- 

 ent, described under the names tabulate, Con. ( = coelata Lea) — 

 assumed as the generic type — from the Upper Claiborne sand 

 and penrosei and dumblei, of Harris, and stantoni Vaughan, 

 from the Lower Claiborne of Texas and Louisiana. Penrosei 

 Harr., which was published by its author as a variety of 

 huppertzi, is in no way closely related to that species, having 

 a radically different embryo as well as a different position of 

 the anal sinus. Dumblei is more slender and has a relatively 

 higher spire and shorter aperture than the others, but does 

 not differ otherwise. Subaequalis, of Conrad, may possibly 

 be an aberrant species of this genus, although the periphery 

 is decidedly more obtuse ; it seems to have the same peculiar 

 minute close-set spiral lines, which, in all the species, alternate 

 with larger lines toward base; it is very stout in form, with 

 short obtuse rounded ribs, the aperture and short slender 

 canal together being fully as long as the remainder of the 

 shell if not longer. The embryo is wanting in the type and 

 apparently only known specimen, which is from the Upper 

 Claiborne sand. A very large and conspicuous umbilicus 

 occurs in tabulata as an abnormal character. 



Microsurcula n. gen. 



This genus is composed of a considerable number of species, 

 all of which are very small, with the body whorls seldom ex- 

 ceeding four in number at maturity. The embryo is relatively 

 large and complex, conical, multispiral, closely coiled and 

 with about five whorls, the lower one to three of which are 



