47 



This species is distinguished by its general form, closed umbili- 

 cus and surface form of the septa. 



Found by R. A. Blair and his accomplished daughter, in whose 

 honor we have proposed the specific name, in the Couteau lime- 

 stone, near Sedalia, Missouri, and now in the collection of S. A. 

 Miller. 



SUBKINGDOM PROTOZOA. 



CLASS PORIFERA. 

 Family RECEPTACULITID^. 



RECEPTACULITES DIXONENSIS, n. sp. 



Plate V, Fig. 21, basal view; Fig. 22, side view. 



Species medium size, general form obovate. Our specimen is 

 more ventricose on one lower lateral side than upon the other. 

 It is a dolomite and the external integument or ectorhim of 

 Billings is not preserved and the internal coating or endorhim is 

 not visible. The part which is presented to us for description is 

 the outer surface of the spicular skeleton. 



The base is broadly rounded and has a subcentral, hard, slightly 

 projecting nucleus from which the sigmoidal rows of rhomboidal 

 depressions arise, and curving, at first, gently to the right and to 

 the left, like the engine turnings on a watch, and then curving 

 upward more rapidly, they make more than one revolution around 

 the skeleton before reaching the edge of the summit aperture. 

 All of the rows originate at the margin of the nucleus, and, as 

 they diverge, they increase in diameter, and then contract toward 

 the summit aperture, abruptly stop without the intercalation of 

 any rows. In other words, the surface is covered with the ex- 

 pansion of the rows of rhomboidal depressions that arise at the 

 small solid nucleus, at the base, some of which do not extend to 

 the summit. Each rhomboidal depressions has, within the elevated 

 marginal lines, a transverse furrow with a central pore and one at 

 each end of the furrow. The transverse furrow is crossed by a 

 less conspicious longitudinal furrow. The central pore is larger than 

 the pore at either end of the transverse furrow. The pores and 

 furrows, probably, represent the spicules which formed the skeleton 

 but have been destroyed. The aperture, at the summit, is sub- 

 central but not well preserved in our specimen. 



In 1861, Prof. James Hall, in a pamphlet report on the Geolog- 

 ical Survey of Wisconsin, page 16, described without illustration 

 a fossil under the name of " Receptaculites globulare" as follows; 



