23 



tial covering of drusy quartz ; the acid resulting from the decomposition 

 of the pyrites subsequently removing the shell, the impressions, which 

 are plainly discernible, showing the forms of the plates of the shell, and 

 the sutures by which they were joined. That the quartzy incrustation 

 took place previous to the removal of the shell, is shown by the spaces 

 which the shell has left being entirely free from crystals. 



The third section of the class of CATOCYSTI is named Scutum by Klein, 

 and Echinanthus by Leske and Phelsum. The shells comprised under 

 this section are of an irregular figure, resembling an oblong or angular 

 buckler. On the base, which is concave, five grooves pass from the 

 margin, and terminate at the mouth in the centre. The upper part is 

 ornamented with five rays, which have been supposed by some to 

 resemble a pentaphylous flower, and by others a five-rayed star. The 

 mouth, which is pentagonal, is furnished with five teeth of an alated 

 form and a plumose appearance, and is placed in the centre of the base, 

 the anus being at the margin. The whole of the surface is beset with 

 minute circular depressions, with central tubercles. 



One genus, Echinanthus, Lesk. comprises all the shells of this section. 

 The first species, Scutum humile, Klein. Tab. xvu. a. -xvin. b. Echinan- 

 thus humilis, Lesk. is rather of an oval form, and is divided into ten area* 

 by five biporous, pentaphyloideal ambulacra, the five smaller areae 

 being comprised in the pentaphyloid surface formed by the ambulacra, 

 and having grooves pass across them, and connecting the immediately 

 opposite pores. Specimens of this species, in a mineralized state, are 

 represented by Aldrovandus, Met. MILS. p. 499, /. I : Scilla, Tab. x. 

 f. 2, 3; Tab. xi. No. 2 : Walch, T. E. V. f. 1, 2. This species is chiefly 

 found in a petrified state in Malta and in Occitania . Dr. Shaw figures 

 a fossil of this species found in the desert Marah, Voyage to Barbary, Sfc. 

 Fig. 40, /;. 128, app. 



As this fossil may thus be seen figured, in its complete state, in the 

 works of these authors ; and as its cast is a more uncommon fossil, and 



