23 



Crania personata of Lamarck) from Shetland and those from the Mediter- 

 ranean is in the thickness and irregularity of the lower valve". The 

 Discina ostreoidcs of Turton is composed, as we have already stated, of 

 two different things (one from the description being an Orbicida and the 

 other from the synonyms a Crania) Fleming has therefore been incor- 

 rect in quoting it only under his Criopus, Fleming has moreover com- 

 mitted a mistake in coining a word, which he has used loithout explana- 

 tion, in his description. Of the signification of this word "areulated'^ it 

 is impossible to form any conjecture; I thought at first that it was only 

 the accidental admission of a supernumerary letter, and that it ought to 

 be read "arcuated;"'^ but when I looked for these two arched, or 

 arcuated, subcentral muscular impressions in a number of upper valves 

 of Crania which lie before me at the moment of writing this, my search 

 was entirely unsuccessful, and I remained ignorant of the signification of 

 his new word. I wish Fleming had condescended to favour us with the 

 signification of several other words which we frequently meet with in the 

 same work, and which, being quite new to us, we cannot perfectly 

 understand. Such things as these are, however, of trifling importance 

 when compared with the interminable mistakes and absurdities which 

 disgrace the History of British Animals, by Dr. Fleming. 



I must now conclude by correcting two other errors which I have 

 committed, both depending upon the same cause as the first. Poli was 

 quite right in identifying Miiller's Patella anomala with his own Criopus. 

 And De Blainville has been mistaken in referring the shell which I 

 found among ballast to Patella anomala of Miiller ; but he has rightly 

 referred it to Orbicula. 



Art, III. A DESCRIPTIVE CATALOGUE of the species of Leach's Genus 

 Margarita. 



§ 1. Testa non umbilicata. 

 1. Margarita taeniata. Testa orbiculari-subconica, tenui, laevis^ima, 

 albida, transversim rufo-vittata ; anfractibus quinque subro- 

 tundatis, ultimo multo majore ; sutura indistincta ; apertura 

 ferfe orbicular!, columella subincrassata, extus depressiuscula ; 

 long. 0-85. lat. 1 poll. Conch, lUustr, Marg. f. 2. 



