1887.] NATURAL SCIENCES OF PHILADELPHIA. 159 



Two names remain of friends, without whose influence and assis- 

 tance this Monograph would probably never have been written. 

 The first has passed the alloted term of "three score years and ten," 

 and now, with failing strength, but unfailing love of his work, is 

 hastening to garner the last ripe sheaves of a life of honorable scien- 

 tific labor. I count it a great privilege to have become acquainted, 

 near the beginning of my Avork, with H. J. Carter, Esq. of 

 Devonshire, England, than whom no obscure scientist could hope 

 for a more constant friend or more courteous correspondent. To 

 the fine artistic skill and unwearying patience of the other. Miss S. 

 G. Foulke of Philadelphia, my readers, with myself, owe a large 

 part of the value of this work, in the admirable drawings from 

 which plates VII to XII have been reproduced. 



These reproductions are the work of the Photo-Engraving Co. 

 (N. Y.) and while it is regretted that from the very nature of the 

 process no j)hoto-engraved plate could repeat, with their relative 

 delicacy, the finer lines of Miss Foulke's beautifiil drawings, in other 

 respects they are very well done. 



