16 



THE NAUTILUS. 



accounts for eleven specimens out of more than sixty. I only had 

 time to note the larger and more conspicuous ones. 



On September 19, 1907, Mr. Bryant made a somewhat similar 

 haul, although less interesting. He most kindly brought the mate- 

 rial to me still alive, and I was able to study it more adequately. 



There were twenty-nine specimens of three species, and all were 

 taken together from the bottom of a floating clam-car. 



The species were as follows : 

 Facelina bostoniensis (Couth.) now Coryphella bostoniensis (Couth.). 



Bergh et auct, al. Europ., " 7 specimens, 4 to 10 mm." 

 Coryphella mananesis (Stimps.). " 2 specimens, 8 mm., 14 mm." 

 Palio lessonii (d'Orb.). " 20 specimens, 1 abt. 12 mm., the rest 

 abt. 5 mm. Seem browner in coloration and much more 

 sparsely tuberculated, with relatively more conspicuous circum- 

 anal tubercles than the European type as figured." 



It will be noted that here again not one is adult, while not one is 

 very young. 



It seems to me that these two captures suggest strongly an au- 

 tumnal condensation of the half-grown Nudibranch population (of 

 certain groups) in moderate depths, just off the shore perhaps, best 

 explained tentatively as a " wave of migration " to deeper water for 

 the winter. It is clear enough how a population, which would be 

 very sparse if spread over the whole area from three fathoms, let us 

 say, to extreme low-water mark, might be much condensed if the 

 cooling waters or failing food supply set them all moving off shore 

 about the same time, only to check and bank up at the edge of some 

 particular deep channel or cold current or on some specially favor- 

 able hunting-ground which all hitherto living anywhere inshore of it 

 must cross. 



NEW MICHIGAN LYMN.EAS. 



BY BRYANT WALKER. 



( Concluded. ) 

 Lymnsea desidiosa peninsulx 



Types (No. 20040 Coll. Walker) from the headwaters of the 

 Union River, Ontonagon County, Michigan. Cotypes in the collec- 

 tions of the Philadelphia Academy and the Chicago Academy of 

 Sciences. Also from Little Iron River, Ontonagon Co., Salmon 



