212 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



scarcity of acanthopores are brought out in tangential sections. The 

 tangential section represented in figures 115 & and c passes through a 

 zone of the zoarium where the acanthopores are best developed. In 

 ordinary tangential sections acanthopores are practically absent. 

 Such sections have few if any characters to distinguish the species 

 from many other Heterotrypidae. In vertical sections, however, 

 both specific and generic characters are well shown. Figure 115 cZ 

 represents a vertical section passing through two layers of zocecia and 

 exhibiting several mature (a) and immature (c) zones, as well as thia 

 zones of accelerated acanthopore development (&). Cruikling of the 

 zoarial walls is likewise well shown in this figure and also in figure 

 115 e, which represents the mature region and part of an immature 

 region of a single zooecial layer. The crenulated zocecial walls give a 

 beaded aspect to the few mesopores which are occasionally developed 

 in the maculae (fig. 115/). 



While StigTYiateTla massalis agrees in growth with a number of Ordo- 

 vician species, it can readily be distinguished by its polygonal, small, 

 thin-waUed zocecia, the zonal development of acanthopores, and the 

 crinkhng of the walls, as mentioned above. 



Occurrence. — ^Apparently rare in the Kegel beds (D2) at Habbinem, 

 Esthonia. 



Holotype.—C&t. No. 57294, U.S.N.M. 



A fragment and thin sections of the type-specimen are in the collec- 

 tions of the British Museum. 



STIGMATELLA INFLECTA, new species. 



Text fig. 116. 



This most interesting species is represented by the type and by sev- 

 eral additional specimens from the Orthoceras and Echinospherites 

 Hmestones at locahties in the Baltic provinces. All of these exam- 

 ples agree in being rather irregularly rounded masses several centi- 

 meters in diameter, cuch as that shown in figure 116 a. The base of 

 the type-specimen, which is of normal growth, is shghtly concave and 

 covered with an obscurely marked epitheca. The other examples 

 have had this epithecated side so overgrown by small, thick-waUed, 

 mesopore-hke ceUs that it is now obscurely rounded and minutely 

 poriferous. Upper celluhferous side of zoarium smooth and without 

 conspicuous maculae, although clusters of large zocecia and more 

 numerous mesopores are present at regular intervals. Zocecial aper- 

 tures in the mature stage irregularly petaloid, due to their indentation 

 by numerous small acanthopores. Where an immature stage of the 

 zoarium is presented at the surface, the apertures are polygonal and 

 without acanthopores. The average zooecium is 0.33 mm. in diameter 

 with four to five in 2 mm. Mesopores are numerous and almost inva- 

 riably isolate the zocecia; they are angular, thin-walled, and fre- 

 quently so large that in the absence of acanthopores the zooecia and 



