FOSSIL CIRRIPEDES. 945 



inwards, straight, or bowed outwards ; tectum strongly convex 

 transversely, not carinate ; basal margin almost rounded to 

 bluntly angular ; in young specimens, as shown by the jDeriods 

 of growth, the basal margin was almost straight; parietes slightly 

 bent inwards, narrow, much less than half the width of the 

 tectum, and marked with almost parallel growth-lines ; inner 

 surface of valve deeply concave for the lower two-thirds, the 

 upper third of the valve being solid and marked with lines 

 of growth, indicating that the valve projected freely to that 

 extent. 



Scuttim (PI. XCV. fig. 2) trapezoidal, umbo situated on the 

 occludent margin about one-third the extent of the valve from 

 the apex ; almost flat to strongly convex ; four-sided, the latei'al 

 or tergal margin slightly longer than the basal margin, with 

 which it makes an angle of about 70° ; the basal margin much 

 longer than the lower part of the occludent margin, with which 

 it makes almost a right angle, the upper and lower portions of 

 the occludent margin making an angle of about 135° ; the upper 

 occludent margin, said Darwin, " homologically corresponds with 

 the tergal margin of the other cretaceous species and with the 

 upper, nearly straight, portion of the occludent margin in the 

 tertiary S. magnimi and the recent S. vtilgareT The edge of the 

 upper occludent margin is upturned and thickened, forming a 

 prominent ridge, with its apex projecting beyond the lateral 

 margin ; a second prominent i-idge extends from the umbo to the 

 basi-lateral angle ; a third ridge, barely perceptible in some 

 specimens, extends from the umbo to the basal margin, near 

 to the rostral angle. On the inner surface there is a deep 

 hollow for the adductor muscle ; along the upper occludent margin 

 the inner surface is slightly raised, which corresponds to the 

 outer thickened ridge, the space between the two ridges being 

 concave ; the inner lidge extends to the umbo, whence it becomes 

 more pronounced and turns inwards, forming a prominent ridge 

 above the hollow for the adductor muscle. 



Tergwm (PI. XCY. fig.. 3) elongately diamond-shape, slightly 

 angular transversely ; the occludent margin is thickened owing 

 to the presence of a ridge on the outer and inner edge, corres- 

 ponding with those on the upper occludent margin of the scutum ; 

 close and parallel to the occludent margin is a ridge which 

 becomes prominent near the scutal margin and extends beyond 

 it; a very prominent straight ridge extends from the apex, and 

 thickens towards the very acute basal angle ; scutal and lower 

 carinal margins almost equal in length, and longer than the 

 occludent and upper carinal margins, which latter are also of 

 almost equal length and together make a right angle. 



Valves of the lower whorl (PI. XCY. figs. 4-8). These are 

 ornamented externally like the scutum, tergum, and carina. 

 The apical half of their inner surface is almost flat and marked 

 with lines of growth, showing that these valves must have pro- 

 jected freely and overlapped the bases of the valves of the upper 



