RISSOA. O 



20. vitrea; 21. pulcherrima ; 22. fulgida; 23. soluta-, 

 24. semistriata ; 25. cingillus. 



It will be seen, however, by the following description 

 of the species, that some of them cannot be placed strictly 

 in one group more than in another. 



A. Cancellated ; outer lip usually strengthened by a rib, and 

 sometimes notched within. 



555> 1. RISSOA STRIA'TULA*, Mteg H- ^ 



Tttrfo striatulus, Mont. Test. Br. p. 306, t. 10. f. 5. .Z?. striatula, F. & 

 H. iii. p. 73, pi. Ixxix. f. 7, 8. 



BODY yellowish-white, with a blood-red mark over the head : 

 mantle forming a small oval lappet or lobe on each side of the 

 neck as in Trochus ; its outer edge is furnished with two thread- 

 like and finely ciliated processes, one at each of the corners 

 of the mouth of the shell, and which project or hang down, 

 seemingly at the will of the animal : snout longish, narrow, 

 cloven at the extremity: tentacles thread-shaped, somewhat 

 flattened on the upper and lower surfaces, with blunt tips ; 

 they are clothed with a very few short cilia : eyes on small 

 tubercles : foot squarish in front, and pointed behind ; when 

 extended it is apparently divided (as in many other, perhaps 

 every, species of Rissod) into two parts, anterior and posterior : 

 opercular or caudal appendage single, rather long, but not 

 projecting beyond the tail or point of the foot ; it issues from 

 beneath the operculigerous lobe : excrement oval, dark-green. 



SHELL conic- oval, with a turreted outline and a slightly 

 twisted base, solid, opaque, somewhat glossy when the surface 

 is not obscured by a mineral coating : sculpture, several laminar 

 transverse ridges, 10 or 11 of which are on the body- whorl, 

 and 3 only on each of the next three whorls ; those encircling 

 the body- whorl are very unequal in size, the 3 uppermost being 

 by far the largest and most apart one from another ; the 3 basal 

 ridges are also widely separated, the intermediate ones being 

 close together ; the uppermost ridge is placed at some distance 

 from the suture ; the interstices of all the ridges are crossed 

 by numerous incurved striae, so as to give the appearance of 

 very fine lattice-work ; these are stronger and more conspicu- 



* Slightly striated. 



