Bulletin - United States National Museum . - weakly sigmoid,concave abov^e, convex below. The umbo is a trifle recurved. The carina is simply arched, more strongly so above; umbo termi-nal. The roof is flat with distinct bordering ribs. The sides aremoderately developed near the umbo, but very narrow basal margin is straight, as are the fine lines of growth across theroof. The upper lateral plate is trapezoidal, the scutal margin much thelongest, concave. The other margins are straight, the carinal shortest,less than half as long as the scutal. The apex is produced in a smalltria
Bulletin - United States National Museum . - weakly sigmoid,concave abov^e, convex below. The umbo is a trifle recurved. The carina is simply arched, more strongly so above; umbo termi-nal. The roof is flat with distinct bordering ribs. The sides aremoderately developed near the umbo, but very narrow basal margin is straight, as are the fine lines of growth across theroof. The upper lateral plate is trapezoidal, the scutal margin much thelongest, concave. The other margins are straight, the carinal shortest,less than half as long as the scutal. The apex is produced in a smalltriangle above and beyond the umbo, which is acute and marginal, onthe scutal side. There is no rostrum. The rostral latus is quadrangular, about as high as wide. The ven-tral and scutal borders are straight, the basal very short. The upper. Fig. 26.—Scalpellum aurivillii. o, b, lateral views x 3; c, S. aurivillii, incertvm lateral VIEW X 2. interior angle is truncated where it comes in contact with the upperlatus for a short distance. The carinal margin is in contact with thecarinal latus, but the suture is more or less covered by the extremelynarrow inframedian latus, which overlies the borders of the plates. The inframedian latus is very narrowly triangular, being wider atthe base. The umbo is apical. It overlies the suture instead of occu-pying a space between the rostial and carinal latera. It is oftenabnormal, as noted below. The carinal latus is twice as high as wide, quadrangular, the umbo at its lower third not projecting beyond the carina. The basal and rostral margins are subequal, straight, and at right angles. The carinal margin is nearly straight, projecting a little in the lower third. 4715—Bull. 60—07 ^ 60 BULLETIN 60, UNITED STATES NATIONAL MUSEUM. The two latera meet below the carina. From the umbo
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Keywords: ., bookauthorun, bookcentury1800, bookdecade1870, booksubjectscience
