108 ANATOMY AND LIFE HISTORY OF MOLLUSCA. 



microscopist, or zoologist, they are such as are equally open to 

 observers elsewhere. This at least is a fact of some interest. It 

 is a negative result, yet requiring more extensive observation than 

 any other path of discovery. I wish to record it here as one 

 result of years of observation, pursued under what must be 

 admitted were exceptional advantages. Having been in the 

 midst of the living animals, and having visited in succession 

 almost every part of the Australian and Tasmanian coasts, I have 

 had ample means of ascertaining what are the facts of the case. 



In recording the above conclusions, it must not of course be 

 forgotten that there are exceptions to this uniformity, and these 

 are of a singularly interesting kind. As an illustration of what is 

 meant, let us take the instance of Trigonia, which, as most people 

 are aware, is a " survival " in Australia of a few species of an 

 almost extinct family, but one which played a most important 

 part in far distant geological times. Now, when Prof. Huxley 

 visited the Australian coast as Assistant Surgeon to the 

 "Rattlesnake," in 1849, he made a special study of the animal 

 of Trigonia, which had been previously described by Messrs. Quoy 

 and Gaimard, but much too briefly. The result is published in 

 the "Proceedings of the Zoological Society for 1849," p. 30, but 

 reveals nothing of any great importance. Messrs. Quoy and 

 Gaimard remark that the disposition of the mantle and the 

 absence of tubes, show a resemblance to the anatomy of the genus 

 Nucula, from which, however, it differs by the disposition of the 

 gills and the brevity of the oral appendages. No other information 

 was obtained, and as far as any bearing on Molluscan problems, 

 it was very disappointing. But if the study of the soft tissues of 

 the animal was barren of results, it was not so with the shell. 

 Anyone who has examined the very beautiful and attractive 

 looking valves of the Sydney species Trigonia lamarckii, Gray, or 

 the much larger Tasmanian species T. 7nargaritacea, Lam., will 

 have noticed the peculiar silky lustre on the outside surface, not 

 unlike " shagreen," but much finer and not so rough to the touch. 

 Mr. Woodward in his " Manual of Mollusca," draws attention to 

 this, and says "that the epidermal layer of the recent shells 

 consists of nucleated cells, forming a beautiful microscopic object." 

 (2nd Edit., p. 431.) The so-called nucleated cells will be shown 

 hereafter to be sense-organs of an elaborate character, and the shell 

 will be seen, from the investigations disclosed in this paper, to be 

 a most interesting object, fully sustaining and even surpassing 

 the interest connected with its geological relations. 



It must also be noted that the peculiarities of the Australian 

 Molluscan Province, whatever they are, are most visible upon the 

 south coast and in Tasmania. There are two elements which 

 mingle with the Australian Marine Molluscan fauna, and which 



