182 PROCEEDINGS OF THE ACADEMY OF [1887. 



7. Sponges in which no gemmulse have yet been discovered 

 and whose classification may therefore be consid- 

 ered doubtful. Urtiguaya, Carter, (Ann. and 

 Mag. etc. 1881. p. 100 and PI. VI. fig. 17.); 

 Lubomirskia, Pallas. Potamolepis, Marshall, 

 (Zeit. fiir Naturwissenschaften XVI. N. F. IX Bd 

 and Taf. XXIV.) ' 

 (Particular attention is invited to the illustrations, from platas 

 prepared by the Photo-Engraving Co. (N. Y.). Plates Nos. V and 

 VI are from original drawings by Dr. C. W. de Lannoy, and repre- 

 sent either the whole or portions of gemmules, with their associated 

 spicules, to explain the typical characteristics of the different genera. 

 They are variously magnified as suited his several subjects. Plates 

 VII-XII incl. are also from original drawings, magnificently executed 

 by Miss. S. G. Foulke. They include altogether thirty-six separate 

 groups, repi'esenting every class of spicules, in an equal number of 

 species or varieties, all equally magnified and drawn to scale. They 

 may therefore be relied upon as depicting the spicules as the student 

 himself will see them : neither diagrammatic nor idealized. The 

 power used was 400 diameters, which has been reduced upon the 

 plates to one half, say 200 diameters.) 



(The measurements accompanying the descriptions of nearly all the 

 North American species are averages resulting from micrometric 

 measurement of from 15 to 30 individual spicules, and may be con- 

 viently reduced to millimeters by moving the decimal point two 

 places to the right and dividing by four. The variability in differ- 

 ent specimens is so great that I cannot regard any meiisureinents as 

 of exact specific value.) 



(I) Gen. SPONGILLA. Carter. 



Part of old genus SpongUla, Auct. (Plate V, figs, i, ii and iii.) 

 Gen. Char. Skeleton spicules acerate, generally smooth, curved, 

 fusiform, pointed ; mostly accompanied by flesh spicules. Gemmu- 

 Iffi globular ; crust variable in thickness or absent altogether ; ac- 

 companied by or charged with minute acerates, (PL V, b.b.b. also 

 PI. VII b.b.) smooth or spined, imbedded in or lying upon it or on 

 the chitinous coat. Modified from Charter. 



When the old genus Spongilla of authors was sub-divided by Mr. 

 Carter in 1881, this term was very appropriately restricted to that 

 type which includes the species most widely diffused and most fre- 

 quently noticed throughout the world. 



