158 



PORIFERATA. 



No. 501. Receptaculites Oweni, Hall. 



This sponge was hollow, of a discoidal, cyliudrical or globular shape, and 

 with a small protuberance near the center of the lower side which is thought 

 to indicate the point where growth began. 



The body-wall has a complex structure. It consists of three layers. The 

 inner and outer integments are composed of numerous rhomboidal calcareous 

 plates, so peculiarly arranged as to give fragments the appearance of an 

 engine-turned watch-case. Numerous small, straight, hollow spicula connect 

 the inner and outer layers. The animal has some points of resemblance to the 

 Foramiuifera. It ranges through the Silurian. Trenton group, Rockford, 111. 



No. 503. 



[1174, Cast]. 

 Syn. 



Siphonia (Hallirhoa) costata, Lamoureux. 



Polypothecia septemloba, Benett. 



The fossil Sponges belonging to this genus, 

 have a comparatively symmetrical form. The 

 body is bulbous and supported by a slender stem, 

 which is composed of very fine parallel longitud- 

 inal tubes, terminating on the surfaces of the 

 central cavity. The base of the stem was fixed 

 by root-like processes. Tlie genus does not occur 

 above the Chalk. From the Upper Greensand, 

 Westminster, England. 



No. 503. [1177, Cast]. Siphonia pyriformis, Goldf. 



These pear-shaped Sponges are from the Upper 

 Greensand, Blackdown, England (a locality which 

 has furnished many very interesting and peculiar 

 forms of Sponges), and are now in the Ward Collec- 

 tion of the University of Rochester. 



Stromatopora . 



This genus forms globular or hemispherical masses of large size. It con- 

 sists of thin concentric laminae, penetrated by minute tubes. The genus 

 ranges from the Lower Silurian to the Trias. This specimen is from the 

 Hamilton Group, near Shueyville, Iowa. 



No. 505. [1185, Cast]. Ventriculites . 



The Ventriculites are the largest group of Cretaceous Sponges. 

 They are shaped like a mushroom or funnel, tapering to a point 

 l)elow, and attached by rootlets. The astonishing complication 

 of their surface is shown by the fact, pointed out by Toulmin 

 Smith, that in one specimen, only three inches high, nine millions 

 of fibres were found! Like Siphonia, this genus is not found 

 above the Cretaceous. From the Upper Chalk of Bridlington, 

 England, and now in the Ward Collection of the University of 

 Rochester. Size, 10 x 3. 



