1887.] NATURAL SCIENCES OF PHILADELPHIA. 159 



I now desire to express my indebtedness. It were idle to attempt to 

 name them all ; but to Professors Allen, Cope, Hunt, Leidy and 

 Heilprin of Philadelphia, to Dawson, Hyatt, Bumpus and Osborn 

 in other localities, I am particularly indebted. As active workers 

 in the same field and during nearly the same period, I am glad to 

 acknowledge my constant obligation to my friends Mr. Henry Mills, 

 of Buffalo, N. Y. and Mr. B. W. Thomas of Chicago, III, whose 

 names Avill frequently be found throughout the following pages. 

 More recently my valued friend and correspondent Mr. A. H. Mac- 

 Kay, of Pictou, Nova Scotia, has been untiring in his efforts, very 

 successful in his local and New Foundland collections and most 

 generous in the contribution of his valuable material. I owe to my 

 friend Prof John A. Ryder of the University of Pennsylvania, what 

 has been of more value than any material, the most unfailing courtesy 

 and the best of advice, assistance and encouragement to persevere 

 in my work. From abroad I have been honored Avith the correspon- 

 dence and publications of Dr. W. Dybowski of Niankow, Russia, 

 Prof Marsliall of Leipsig, Vejdovsky and Petr of Prague, Bohemia. 

 Prof Vejdovsky has laid me under especial obligations by his repeated 

 gifts of Bohemian and other European sponges, besides his "Diagnosis 

 of the European Spongillidae" now published as a very valuable 

 contribution to this paper. I thank Dr. C. W. de Lannoy, late of 

 Chester, Pennsylvania, for the original draAvings for plates V aud 

 VI the excellence of which wdl be conceded by all acquainted 

 with the subjects. 



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 work, 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 Avork, in the admii-able 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 



