118 THE NAUTILUS. 



loosen it, and the projecting siphonal portion was usually 

 covered with soft silt. 



The one hundred specimens collected at random from this 

 colony were very uniform in size. A typical shell has the fol- 

 lowing measurements: length, 140 mm.; height from margin to 

 hinge, 80 mm.; diameter, 55 mm.; thickness of the individual 

 valve, 2 mm. A comparison of these measurements with those 

 given by Simpson (Cat. p. 428, 1914) for this species shows the 

 average Colorado specimen to be almost one-half longer than 

 specimens from the type localit}^ Topeka, Kansas. Moreover, 

 a few shells from Black Wolf Creek are 180 mm. long. Only a 

 few juvenile specimens were found, the smallest of these meas- 

 uring 70 mm. in length. These small specimens are of a 

 brilliant green color and have a more or less definite pattern of 

 rays. The adult shells were a rich, pitchy black when first 

 taken from the water and as dried and cleaned specimens they 

 have a polished or varnished appearance. The umbonal half of 

 each valve is black or greenish black, and the marginal half a 

 bistre brown, the color transition between the two portions of 

 the shell being rather abrupt. The soft parts of the adults were 

 also highly colored, among the individuals collected two forms 

 not correlated with sex, were evident : a bright salmon-pink 

 type and a dull chocolate-brown type. 



While cleaning the shells it was noted that most of the 

 females were distended with eggs. Many shells contained large 

 irregular pearls, several of which were at least 15 mm. in 

 length. These pearls were invariably irregular and more or 

 less attached to the shell. Although their lustre was excellent, 

 showing a good deposit of lime, they were very frail. Several 

 were opened and found to contain masses of blue clay like that 

 in which the mussels themselves were found. Ranchers living 

 along Black Wolf Creek told of several freshets during the past 

 three years which swept out numbers of shells from the deep 

 water back of dam. It is possible that these mud pearls may 

 have been caused by the sudden introduction of mud into the 

 shells during these floods. 



It may be added that there is a large specimen of Anodonta 

 in the Museum of the University of Colorado marked Anodonta 



