53 



little if any better, led him to think it doubtfully referable to U. luteo'iis, * from 

 some forms of which the females are not easily distinguishable. Three out of 

 four shells sent to a conchologist in Cincinnati were referred to U. radiatus, 

 while the remaining one was considered a specimen of U. luteolm. The shells 

 were really not in a condition to admit of being properly determined. Not until 

 October of the past year did I succeed in collecting specimens which had the 

 undulations of the beaks well preserved. I was led to go out so late in the 

 season by a letter from Mr. A. F. Gray, relating to the shell in question, of 

 which I had sent him specimens a short time previously. He regarded as correct 

 my views that it differed essentially from both U. luteolus and U. radiatu.s, but 

 thought that further study and comparisons might prove it to possess affinities with 

 some other described species, and expressed a wish to see a large series of the best 

 shells I could obtain. On my next holiday I went down the river to Duck Island 

 and collected a number of male and female shells, including a few in fine condi- 

 tion. I despatched these to Mr. Gray on the day following, but beard nothing 

 more about them, until February 28th, when I received the pleasing, though not 

 unexpected information that the shell was undoubtedly a new species. The 

 names U. bellus and U. hurealis were suggested as appropriate. The latter seems 

 the more fitting, and the species shall accordingly be known as Unio boreaUs, A. F. 

 Gray. A description, promised at my request, has not yet been received, and I do 

 not wish to describe the shell to-night, lest I should in any way interfere with 

 the priority of my friend's description. The right of naming U. borealis belongs, 

 to Mr. Gray, as he was the first to recognize its specific distinctness from any 

 described unio. 



[Mr. Gray's description was received some time after the reading of my paper 

 and is here given in full : 



liNio Borealis, — A. F. Gray. 



Shell smooth, broken only by numerous ridges of growth ; obovate, 

 very much inflated in the female form, the male more compressed, very 

 inequilateral, obtusely angulated behind and rounded before, the basal or 

 ventral margin rounded, beaks badly eroded and but slightly raised ; 

 ligament thick, moderately long and dark|[brown ; umbonal slope flattened, and 

 but slightly carinated ; epidermis variable, some specimens dark olivaceous 

 brown with broad obscure rays of dark green, others yellowish green with numer- 

 ous fine rays of a brighter green, cardinal teeth rather large, somewhat compressed 

 and corrugate ; lateral teeth thick, slightly curved, and with crenulate margins ; 

 anterior cicatrices distinct, that of the adductor muscle very deeply impressed ; 

 dorsal cicatrices posterior to the centre of the cavity of the beaks ; posterior 

 cicatrices confluent and but slightly impressed; cavity of the shell deep and 

 rounded ; cavity of the beaks obtusely rounded and deep ; substance of shell 

 very thick, thickest before ; nacre usually white, occasionally rosy, and some- 

 times a beautiful pink, and beautifully iridescent. 



Transverse diameter, 3-15 inches; altitude, 1-95 inches; lateral diameter, 

 1-65 inches. These measures are from a large female. A male shell measures: 

 transverse diameter 3-15 inches; altitude, 1-90 inches ; lateral diameter, 1-35 

 inches. 



For this beautiful shell, and the privilege of describing it, I am indebted to 

 Mr. F. R. Latchford, from whom I received quite a large series of this Unio, 

 which belongs to the group of which Unio luteolus of Lamarck may be considered 

 the type. It difters from that species in being shorter transversely, in Laving a 

 much thicker shell and having the beaks badly eroded. In its outline it bears a 



* After the above was writen, I sent some young specimens of U.boreaUs,A. F. Gray, to 

 Mr. Tryon, and they have convinced him, he iaforms me, that tae species is new. 



