252 Miscellaneous. 



Note to Dr. C. A. White's Paper. By R. Ellsworth Call. 



In Dr. C. A. White's interesting communication " On the Anti- 

 quity of certain Subordinate Types of Freshwater and Land Mol- 

 lusca," occur two slight errors which may be misleading to future 

 students pursuing the same line of research. On p. 250 he lists 

 seven species of fossil ITnionida? from the Laramie strata of Wyo- 

 ming and Utah, together with a second series of seven recent 

 Unio ties " as their respective congeners." Congeneric with the U. 

 Couesi, White, is written Unio complanatus, Solander. Since the 

 Doctor gives a list of Unionidae inhabiting the '■'•waters of the Missi- 

 sippi basin " as congeneric with the fossil forms, U. complanatus, 

 Sol., is out of place in sucb a list, being an inhabitant solely of the 

 Atlantic slope, together with the numerous other species of which 

 it is a type. This species is not found west of the Alleghanies. 

 This fact is important in the matter of the geographical distribution 

 of the recent Unionidae. A slight error in the determination, or 

 the nomenclature, of the species placed as congeneric with U. End- 

 lichi, White, occurs. Dr. White evidently means Unio gibbosus, 

 Barnes. Unio gibbus was described by Spengler in ' Skrivter af 

 Katurhistorisk Selskabet,' vol. iii. (1792); and the habitat given is 

 Tranquebar. — Arner. Journ. Sci. August 1880, p. 158. 



Dexter, Iowa, July 6, 1880. 



On the Metamorphosis of Prosopistoma. By M. A. Vaysslere. 



In August 1878 I had the honour of presenting to the Academy, 

 in conjunction with Dr. E. Joly, a note on the organization of 

 Prosopistoma punctifrons. We had at our disposal for the investi- 

 gation, of which we published a summary, a considerable number 

 of living specimens ; and nevertheless we were unable to observe 

 any transformation in these curious insects. We were thus led to 

 adopt the opinion of Mr. M'Lachlan, and to assume with him that 

 Prosopistoma is only an Ephemerine adapted to a permanent 

 aquatic existence. Our anatomical observations, and more espe- 

 cially those relating to the considerable concentration of the ner- 

 vous system, seemed to confirm this hypothesis. 



It must, however, be decidedly rejected, as on the 3rd of June I 

 was able to witness the metamorphosis of two Prosopistomas cap- 

 tured in the Rhone near Avignon in April last. 



The following are the principal phases of this metamorphosis. 

 Towards the end of last month (May) the amber-yellow colour of 

 some of the insects which I kept in captivity became darkened ; 

 I could then soon perceive through the skin the first lineaments of 

 the new individual ; and two or three days afterwards the animal 

 cast off its nymphal envelope. To free itself from this the insect 

 employs the same processes as the other Ephemerine types. 



In the perfect state Prosopistoma very exactly resembles Cosnis, 

 and consequently belongs definitely and indisputably to the family 

 Ephemerinas ; its last segment is furnished with three rudimentary 

 setae, representing the natatory seta? which it possesses in its 

 aquatic states. The anatomical modifications superinduced by this 

 metamorphosis will be studied hereafter in a complete monograph 

 of this genus. — Comptes Rendus, June 7, 1880, p. 1370. 



