TRIGONIA. 



only from New Holland : we suppose it to be marine^ but 

 have no certain information upon that subject. It was 

 first published in the Annales du Museum^,''^ vol. 4, 

 under the name Trigonia margaritacea, but Lamarck, 

 without giving any reason, has altered its specific name 

 to pectinata, in his " Hist. Nat. des Anira. sans vert." 

 We have retained its former name, merely on account of 

 its priority. It has regular tubercular ribs diverging from 

 the umbo and a thin epidermis. 



By far the greater number of species of this Genus 

 are either ribbed on the outside, or covered with tubercles 

 placed in regular or interrupted series; a few are only 

 slightly grooved iu their young state, or at the rounded 

 side. " ..^i.^,, i.\ 



The fossil species are numerous, tliey^ occur in the 

 Lias, the upper and lower Oolites, and throughout the 

 Oolite series of Phillips and Conybeare; and several spe- 

 cies occur in the beds of Green Sand. Those that are 

 found in the Tisbury beds of Portland Rock, frequently 

 have the ligament remaining. We should have been much 

 disposed to doubt the probability of any species occurring^ 

 in strata above the Green Sand, if Miss Salisbury had 

 not shown us one which she dug out with her own hands 

 at Muddiford: notwithstanding this fact, the Trigonia 

 may be said to characterize the beds below the Chalk, and 

 above the Lias. j oj m u v/vi* v/t . - 



^jviiiv OHO 'r' " ?,on\mcs 



Mods 



