| OCR Text |
Show 1904.] FROM EAST AFRICA AND ZANZIBAR. 383 The following notes on the principal divergencies presented have no pretension to be exhaustive, but may perhaps prove useful. 1. A s a rule the shape is somewhat high, elongated, and limaci-form, with a narrow mantle-edge, but some species are low and distinctly oval, with the mantle-edge very wide and ample. Such are Chr. reticulata, sykesi, cctvce, and annulata here described; and it would appear from the published plates and descriptions that Chr. albescens, iheringi, punctilucens, histrio, propinquata, splendens, albo-pustulosa have a similar shape. Some species (e. g. Chr.r vicina) are capable of assuming two forms-one high and narrow, the other flat and oval; so the distinction in shape may perhaps not be absolute *. 2. The skin is usually soft and smooth, but the dorsal surface bears tubercles in Chr. orsinii, sannio, pustulous, verrucosa, lapinigensis, and the somewhat doubtful roseopicta of Verrill. The very abnormal Chr. scabriuscula is spiculate with hard lumps. 3. Chr. runcinata, pantharella, sannio, piclurata, camce.no, elegans, glauca, californensis, gonatophora, sycilla, have small knobs, apparently of a glandular character, on the underside of the mantle-margin. 4. The colour is hardly ever uniform. There is usually a coloured border (sometimes double) round the mantle-edge, and generally a pattern on the back formed of stripes or spots. Although this pattern may vary considerably within the species, the spotted and striped forms appear to be distinct. Sometimes, bowever (e. g. in Chr. runcinata), spots arranged in a line unite to form a stripe, and Chr. semperi and nigrostriata appear to be the same, except that the first is spotted and the second striped. It would be rash in the present state of our knowledge to make any general statement as to the correspondence between these two types of pattern and other characters, but in a considerable number of species stripes are combined with an elongate form and bifid teeth, with or without accessory denticles under the bifurcation (e. g., Chr. ccerulea, gracilis, messinensis, sycilla, cornea, hilaris, lineata, marenzelleri, thalassopora, lapinigensis); while another combination, of an oval form, spotted pattern, and teeth bearing many denticles but not bifid, is presented by Chr. reticulata, sykesi, cctvce, annulata, punctilucens, splendens, and histrio. Elongated spotted forms are not uncommon, but none of the oval forms with ample mantles as yet recorded are striped. 5. The branchiae range from 5 to nearly 30 in number, and are variously arranged in a complete circle, or a circle more or less open behind or a double spiral (see Plates XXIII. figs. 2 & 8 ; X X I Y . fig. 2). Sometimes the plumes are uniform in size ; sometimes those in front (more rarely those behind) are larger. Typically they are quite simple, but frequently some are bifid and sometimes several branches are developed (e. g. Chr. tryoni and striatella). But when this occurs the ramifications are thin and irregular, and * [I observed this change of shape in some of the species here dealt with during life.-C. C] |
