49 



facilities of which I had ample leisure to avail myself during the midsummer 

 vacations. 1 have in my spare time since then studied carefully these 

 humble creatures ; and, not content witli my own determinations, have take 

 much pains to have the species collected identitied hy the best authorities. All 

 have been checked or named by such eminent conchologists as Mr. Arthur F. 

 Gray, of Danversport, Mass , Mr. Geo. W. Tryon, of the Academy of ISciences, 

 Philadelphia, and Prof J. F. VV^hiteaves, F.G.S., of the Geological Survey of 

 Canada. I am therefore morally certain that, except perhaps in one or two 

 instances, the shells which I found have been correctly determined. 



The species met with belong to the genera Unio, Margaritana, and AnoJonta. 

 These are distinguished from one another more by the conformation of their shells 

 than by any peculiarities ot the animals themselves. Hence it is of tlie shells 

 alone that most works on the Unionidse treat ; and from this course it is not my 

 intention to depart at present. The shell itself will always enable the student 

 to distinguish one species from another. But the soft parts are by no means 

 undeserving of attention. In species of the same group they are very much 

 alike. In species of different groups, for instance in U. rectus and U. occidtns, 

 they are so di8^imiIar that the leatt practised eye can perceive differences in their 

 form and arrangement. In all cases they present the same admirable 

 ordination of structure to purpose that we see elsewhere throughout the works 

 of nature's God. Even the distribution of the Unionidaj is provided for, by their 

 young being for a time endowed with hooks by which they can attach themselves 

 to contiguous objects, often a fish or a water-bird, and be transported far from 

 their place of birth. In the winter and spring the young, having already well 

 formed shells, are extruded from the branchial uterus of the females in hundreds 

 of thousands and even millions. According to a computation made by Dr. Isaac 

 X,ea, of Philadelphia, who has during fifty years studied the Unionida;, and 

 described almost half the species known, a large specimen of U. Multiplicatus, 

 Lea, contained upward of three millions of embryonic young. Nearly all perish 

 early in their free life, being devoured by fishes, crustaceans and the larva; of 

 many kinds of insects. Few, accordingly, attain maturity, which is reached in from 

 six to fen years. Their food consists of animalculfe, which the water flowing in 

 through the branchial orifice coveys to the mouth, at the same time that it 

 supplies oxygen to the lamelliform gills. 



Of the species found in the vicinity of Ottawa the first to be noticed belong 

 to the genus t'/»o. Shells of this genus are readily distinguishable from those 

 of the genera Margaritana and Anodorita, by their having both cardinal and lateral 

 teeth. The genus, according to Jeffrys, was estabished by Phillippson in 1788' 

 Tjut it is generally attributed to Retz, who was chairman of the meeting at which 

 Phillippson read his essay sisUns Nova Testaceorum Genera. 



TJnio complanatus, Solander, is abundant in almost all our streams and lakes, 

 and is subject to much variation in size and colouring. What may be regarded as 

 the typical form is common in the Rideau everywhere and in the Ottawa above 

 the Chaudiere Fall?. It is a moderately thin," brown, depressed, sub-rhomboidal 

 shell, with a nacre of different and often of exceedingly beautiful shades of purple 

 The average dimensions of ten shells, five from each river, are as follows : length 

 3-5 in., height 1-7, diameter 0-8. 



In company with the typical form, I found near Skead's Mills, in 1880, a 

 specimen of a small variety which is of considerable interest. Although present- 

 ing every appf-arance of maturity, it is only an incli in height by two and a half 

 in length. For its size it is very thick and rtgnlarly inflated. I am informed 

 that a similar variety occurs in some streams in Western New York. 



A form almost a§ Fmall is found in the cold and limpid waters of Metch's 

 Lake. But it is a thin and not a thivk shell : not infl ted but depressed. Its 

 colour is a very light brown. 



