214 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



mature and immature zones and shows on the left-hand side the po- 

 lygonal zooecia without acanthopores surrounded by mesopores often 

 of so nearly the same size that there is difficulty in separating the two. 

 In the central part of the figure a macula of mesopores occurs, while 

 on the right hand side the initial development of acanthopores at the 

 base of a mature zone is figured. The normal occurrence of the acan- 

 thopores in the fully matured zone is illustrated in figures 116 c and d. 



Occurrence. — Rare in the Orthoceras limestone (B3) at Port Kunda, 

 Esthonia, and in the Echinospherites Hmestone (Cl) at Pulkowa and 

 at Archangelski on the Wolchow River, government of St. Peters- 

 burg. 



Eolotype.— Cat. No. 57295, U.S.N.M. 



British Museum, two sections of the type-specimen and one speci- 

 men from Pulkowa. 



STIGMATELLA FOORDU (Nicholson). 



Text figs. 117, 118. 



Callapora foordii Nicholson, in Nicholson and Lydekker, Man. Pal., vol. 1, 

 1889, p. 351, fig. 229. 



I was fortunate enough to find a single specimen of this interesting 

 organism in the collections^ from the Kuckers shale. Baron Toll's 

 estate. The species can hardly be said to have been described, and, 

 moreover, Nicholson gave no horizon and locality other than "Ordo- 

 vician rocks of Esthonia," but his figured thin sections are so distinc- 

 tive that I have no doubt of the correctness of the present identifica- 

 tion. Both his remarks concerning the species and his figures are 

 reproduced below. In the description of his figures, I have also 

 copied Nicholson's wording, although the corresponding terms used 

 in the present paper are inserted in brackets. 



The great majority of the Monticuliporoids exhibit no radial structures in the tubes 

 which could be compared with the ' ' septa " of an ordinary coral. In a few forms, such 

 structures do occur, but it is doubtful if in any such instance we have to deal with 

 structures really developed in mesenteries, and therefore really homologous with the 

 "septa" of the Zoaniharia. Thus in Fistulipora each autopore is provided with two 

 longitudinal folds, situated opposite one another, toward one end of the visceral cham- 

 ber. Again, in a hitherto xmdescribed species of Callopora each autopore is provided 

 with from two to five radial plications of the wall, which closely resemble the "septa" 

 of Tetradium, and give a characteristic floriform appearance to cross sections of the 

 corallites. 



As may be readily imagined from the foregoing notes by Nicholson 

 his main object in introducing figures of Callopora foordii was to 

 show the occurrence in certain monticuliporoids of radial plications 

 closely resembhng the septa of typical corals, and consequently indi- 

 cating the affinities of Monticulipora and its allies with the corals. 

 However, he failed to note that a small acanthopore is present at the 

 end of each fold and that the present species is therefore only an exag- 

 gerated case of indentation of the zooecial cavity by the acanthopore 



