PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 97 

 Geuus CAMPELO:\rA Eafiiiesque. 



Campeloma prodticta (sp. nov.), Plate III, figs. 7, 8, and 9. 



Shell, elongate-ovate; test, uioderately tbick; spire, more than nsnally 

 produced for a species of this geuus; volutions, six or seveu, usually 

 slightly flattened, or having a faint revolving <lepression upon the dis- 

 tal side near the suture, which is more apparent upon the larger than 

 the smaller volutions; suture, deep and abrupt upon the proximal side: 

 aperture and lips having the usual characteristics of Campeloma; sur- 

 tace marked by the usual lines of growth, and by somewhat numerous 

 revolving stride which are often obscure. Among these examples are 

 others which possess the general characteristics of those Avhich are re- 

 garded as the types; but two or three of the revolving striic upon th(^ 

 smaller volutions of these examples are much more prominent than in 

 the case of typical examples. I at present, however, regard these as 

 only varieties of a very variable species. 



Length of aji example regarded as typical, 32 millimeters ; breadth of 

 the last volution, 14 millimeters; but some examples, evidently referable 

 to the typical forms, are pro]»ortionally less elongate. (Museum No. 

 8140.) 



Position and locality. — Laramie strata in the Valley of Yellowstone 

 River, Montana, where they were collected several years ago by Mr. J. 

 A. Allen. 



The under valve of Anomia micronema JlFeel'. 



It has been the subject of frequent remark that not a single example 

 of the under valve of either of the two species of Anomia^ A. micnmemef 

 and A. (jryphorhynclms Meek, both of the Laramie Group, has ever been 

 discovered, althougli hundreds of examples of the upper valves of troth 

 of these species have been obtained, at many different localities, in a 

 good state of preservation. I was lately so fortunate, however,, as to tind 

 in the Laramie strata of Northeastern Colorado several examples of the 

 under valve of A. micro7iema^ one of which is illustrated by fig. 3, 

 Plate 111. That the under, or byssus-beariug, valves of A. mieronema at 

 least have been so generally destroyed is due to the f}»ct, first, of their 

 extreme thinness, and, secondly, to the fact that, with the exception of 

 a thin, porcelanous layer in the middle portion, the whole valve is^ com- 

 posed of a prismatic layer, like the shell of Pinna ; the pearly layer, 

 which gis^es such strength to the upper valve, being apparently entirely 

 wanting in the lower. This prismatic layer breaks up into its compo- 

 nent prisms with great facility. The characteristics of the under valve 

 of A. mieronema, as well as those of the upper valve, show it to be a 

 true Anomia ; thus presenting evidence of the great antiquity Osf the 

 genus essentially as it exists to-day. 



Both valves of recent species of Anomia have, as a covering toithe 

 pearly layer, a very thin prismatic layer, which is often obsolete. This 

 layer is also sometimes distinguishable upon the upper valvef? ©#' these 

 Proc. Nat. M us. 82 ^7 June 94, 1 8 82, 



