times attains, a specimen trom the canal beyond Hartwell's Locks measuring 

 5-5 in. in length, 3-4 in height, and 2-2 in diameter. It bears some resem- 

 blance in outline to U. occidens of which Say considered it only a variety. His 

 opinion on this point is now held by very few ; and I hardly think that anyone 

 who compares the two as they here occur would care to pronounce them speci- 

 fically identical. U. subovatus, is less inflated than U. occidens, and less approxi- 

 mate at the beaks, while with respect to beauty there is no comparison between 

 them. 



On the valves of this and other large species in the Rideau River I have 

 observed — besides the curious spiral follicle of the larva of a phryganaceous 

 insect, Ilelicopsyche arenifera, which was first described as a mollusk of the genus 

 Valvata — a small isopod crustacean, which is worthy of note as being probably the 

 best living, though degenerate, representative of the trilobites that ouce abounded 

 here on the low tidal fiats of the Silurian seas. It is I think the species de-cribed 

 by De Kay as Fluvicola Ilerrickii. 



Unio alatus, Say., was found here by Mr. Heron in 1880, at d was 

 recorded from this vicinity twenty years ago, by Mr. Whiteaves in a valu- 

 able paper published in the Canadian Naturalist. There are a few speci- 

 mens in the museum of the Ottawa Literary and Scientific Society, which 

 were probably collected by the late E. Billings, the palaeontologist. As I have 

 not met with it on my many excursions, I think it must be rare, or at least re- 

 stricted to a small area. It is the only species found here in which the wing 

 rises higher than the right line of the hinge margin. It occurs from Georg a to 

 Vermont and westward to Nebraska and Manitoba. Certain other species as U. 

 ^pinosus, Lea,, and U. Shepardianus, Lea, are confined within narrow limits to one 

 btream. 



Unio gracilis, Barnes, is another winged species which has not, till now, I 

 believe, been recorded from any locality in Canada east of the Welland Canal. 

 It is not at all commoti, Mr. Poirier and m3'^self having found only five or six 

 specimens during the summer. These were collected on sand bars near Kettle 

 Island. It is an exceedingly thin and fragile, depressed, snb-triangular shell, of 

 a greenish yellow color. The hinge margin is straight and prolonged into a 

 large wing, '.miting the two valves. It may be distinguished from U. alatus, by 

 its greater fragility, lighter color, both inside and out, and by its differently 

 formed wing. 



Unio pressus, Lea, was found by Mr. Tyrrell, of the Geological Survey, in the 

 llideau near the Rifle Range. Only one specimen was met with, and that he has 

 with great kindness presented to me. It is but little more than two inches in 

 length, very much flattened, and the hinge margin is straight with a slight 

 alated projection. The beaks are finely undulated. Its form, its internal and 

 «xternal color, together with the shape of its cardinal teeth, seem to connect it 

 with the margaritanie. 



Unio Canadensis, Lea, was originally described from the St. Lawrence near 

 Montreal. Both Mr. Tiyonand Mr. A. F. Gray have referred to this species some 

 shells which I collected in Nepean Bay. Mr. Gray writes : " It seems to agree 

 well with the characters of U. Canadensis, and with Dr. Lea's figure. From these 

 data, and without a typical shell with which to compare it, I am justified, I think, 

 in referring it to that species." Mr. Tryon says : " I regard a shell which you sent 

 me from Nepean Bay as the true U. Canadensis.''' It appears to be rare, only a 

 few specimens having been found. It is of an oval shape and dark olive colour, 

 with indibtinct rays. • 



Unio horealis, A. F. <7ra?/, is a new species. It occurs in the Ottawa, from the 

 mouth of Brigham's Creek to Templeton, ai d j)robably much farther down. 

 Although common, it is very seldom met with in good condition. 



I first submitted this shell to Mr. Tryon, but the only spetimrns I had to 

 send were so badly eroded that they could not be determined. .V second W, 



