2 REPORT 1856. 



Fig. 5. Fissurella rugosa, Sby., including F. chlorotrema, Mke., F. hwnilis, Mke., 

 and F. viminea, Mke. non Rve. : a, finely grown, with faint, flattened, 

 smooth ribs, and trilobed hole ; b, normal state, ribs faint, hole suboval ; 



c, specimen of irregular growth, normal outline when young, ribs stronger ; 



d, specimen with ribs on the upper portion strongly developed ; e, speci- 

 men of coarse growth, ribs nodulous ; /, extreme form, from which the 

 species was described, ribs very strong and irregular. The colour varies 

 from uniform green to nearly uniform red ; the young shells being gene- 

 rally green with a red patch, g, h, i, fc, interior sketches of hole and cal- 

 losity. The shape of the hole is generally a very constant character in 

 Fissurellidce. 



PLATE VIII. 



Fig. 1. Development and varieties of Crepidula nivea, C. B. Ad., including Calyptrcea 

 squama, Brod., Calyptrcea Lessonii, Brod., and Crepidula striolata, Mke. 

 (=Crypta nivea, Ianacus squama, and Ianacus Lessonii, H. & A. Ad.) : 

 a, inside view of very young specimen, deck just forming ; b, ditto, a 

 stage older; c, ditto, older, less magnified, anterior sinus not developed 

 (Crypta, H. & A. Ad.); d, external view, showing prominent, ribbed 

 apex; e, another specimen, rayed (squama, Brod.);/, group of deck- 

 margins, the horizontal line representing the medial point ; the two to 

 the right are young, magnified ; the rounding of the outline and develop- 

 ment of the anterior sinus, made of subgeneric importance by Messrs. 

 Adams, here appear extremely variable; g, a normal specimen, margin 

 sharp ; h, the same indented by attachment to a Strombus granulatus ; i, 

 margin in layers, flattened, abnormally thickened near the umbo ; j, out- 

 side view, form striolata, the layers beginning to appear separate outside; 

 k, layers here and there prominent, form Lessonii, shell concentrically- 

 striated, and with colour rays as in e ; Z, an abnormally bilobed specimen, 

 form Lessonii ; m, a specimen abnormally costated, by attachment to a 

 ribbed shell ; n, inside view of two specimens, laid with the deck-margin to 

 correspond, to show the great length of deck in the lined specimen, and 

 its shortness in the dotted one ; o, two specimens similarly laid, one long 

 and straight, the other rounded and semispiral, like Crepipatella, H. & 

 A. Ad. ; the long specimen has grown in the burrow of a Lithophagus, 

 and displays margin-layers at the umbonal region, and one Lessonioid 

 lamina in front ; p, profile of the last-named specimen, with deck promi- 

 nent, and back somewhat indented, as in C. explanata, Gld. 



Fig. 2. Young state of Crepidula unguiformis, Lam. (Ianacus, II. & A. Ad.), to com- 

 pare with the last species, which it closely resembles when adolescent : a, 

 inside view, showing large imbedded spiral portion ; b, outside, showing 

 flattened, smooth spire. 



Fig. 3. Crepidula aculeata, Gmel., including Calyptrcea echinus, Brod., Calyptrcea 

 hystrix, Brod., Crepidula Californica, Nutt., and probably Crepidula 

 costata, Mke. (not Sby.), subgenus Crepipatella, H. & A. Ad. : a, young 

 state, like Neritina, deck just commencing ; b, ditto, a stage older ; c, the 

 same in profile ; d, ditto, somewhat older ; e, ditto, a little older ; f, out- 

 side view, older, showing spiral growth, margin not produced, spines just 

 appearing ; g, a group of deck-margins, arranged as in fig. If, the three 

 to the right being magnified ; the second from the left is the normal state ; 

 in the first, not only the characteristic medial angle is rounded off, but an 

 abnormal angle appears, turned the wrong way ; h, two specimens, out- 

 side view, to show straight and spiral growth, as in fig. 1 o ; i, two speci- 

 mens, laid with the upper margins corresponding, to show dispropor- 

 tionate length of deck ; the short deck belongs to the dotted margin ; 

 j, two specimens in profile ; one arched, with deck internal ; the other 

 (dotted) flat, with deck prominent. 



