MOUTH. 41 



supra-cesophageal cavity, is generally furnished with small, 

 often bead-like teeth. The Palpi are small, their apices 

 never actually touching each other; they are more or 

 less blunt, not differing much in shape in the different 

 genera (PL X, figs. 6 to 8), and clothed with spines. They 

 are not capable of movement ; their function seems to be 

 to prevent prey, brought by the cirri, escaping over the 

 labrum ; I infer this from finding in Anelasma and in 

 the male of Ibla, which have the cirri functionless, that 

 the palpi are rudimentary. 



The Mandibles (PL X, figs. 1 — 5) have from two to 

 ten strong teeth in a single row ; where the number 

 exceeds five, several of the teeth are small; the in- 

 ferior angle is generally pectinated with fine spines; 

 in Lithotrya (fig. 2), the interspaces between the teeth are 

 also pectinated. In the same individual there is not un- 

 frequently one tooth, more or less, on opposite sides of 

 the mouth. Internally, the mandibles are furnished on 

 their outer and inner sides with several ligamentous 

 apodemes, (in Lithotrya roughened with points (PL X, 

 fig. 2), for the attachment of the muscles ; of these (fig. 1), 

 there is a chief depressor and elevator, attached at their 

 lower ends to near the basal fold of the mouth, and a 

 lateral muscle, attached to the broad basal end of the palpi, 

 and serving, apparently, to oppose the edge of mandible to 

 mandible. The Maxilla in the different genera (PL X, 

 figs. 9 to 15) differ considerably in outline ; they are gene- 

 rally about half the size of the mandibles ; at the upper 

 corner, there are always two or three spines larger than 

 the others, and often separated from them by a notch ; 

 the rest of the spinose edge is straight, or irregular, or 

 step-formed, or with the lowest part projecting, or with 

 one or two narrow prominences bearing fine spines. All 

 these spines, quite differently from the teeth of the man- 

 dibles, are articulated on the edge of the organ, and stand 

 in a double row. At a point corresponding with the 

 upper articulation of the mandibles, a long, thin, narrow, 

 rigid apodeme, projects inwards (fig. 10), and running 



