122 BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 



on a median prominence of the frontal. The avicularium is short, triangular, with- 

 out pivot, with its beak turned toward the top. The dietellae are not entirely 

 covered over, and appear between the zooecia in the form of small slits. The 

 ovicell is large, globular, buried in the distal zooecium, covered with a tremocyst. 



-,, . A . f7i,a = 0.10 mm. „ . (L2 = 0.60mm. 



^leasurements. — Apertura , . ,„ _ ,„ zooecia, _ ._ 



^ [Za= 0.10-0.12 mm. [(0 = 0.50 mm. 



Variations. — In this genus, where the species are so difficult of determination, 

 the present species is very well characterized by the dieteUae not entirely covered 

 over by the tremocyst. We are ignorant as to the cause of this remarkable pecu- 

 liarity, which has been observed hitherto only in the Membraniporae. The distal 

 diatellae are visible on the marginal zooecia. The two proximal spines are always 

 larger and more salient than the distal spines. Our micrometric measurements are 

 those of the larger zooecia for the variations are considerable. 



Occurrence. — Miocene (Yorktown) : Near Macedonia Church, Essex County, 

 (very rare) ; 1 mile northeast of Suffolk, 3 miles southwest of Petersburg, and other 

 localities in Virginia. Miocene (Duplin marl): 10 miles south of Greenville, North 

 Carolina (rare). 



Cotypes.—C&t. Nos. 68593, 68594, U.S.N.M. 



MICROPORELLA TESSELLATA Tuomey and Holmes, 1857. 



Plate 30, figs. 2, 3. 



1857. Cellepora tesselata Tuomet and Holmes, Pliocene fossils of South Carolina, p. 13, pi. 4, fig. 7. 



-,<• I i , fAa = 0.06mm. „ . (i2 = 0.75mm. 



Measurements. — Apertura , „,, Zooecia , „ „„ 



I fa = 0.11 mm. [Z2 = 0.60mm. 



Variations. — There are often six very short and very inconstant spines. The 

 vestibular arch is always visible. The apertura is relatively small for so large a 

 species, which appears to indicate extremely fine tentacles. The frontal is per- 

 forated with rather large tremopores. The ascopore is surrounded by a salient 

 peristome. In the vicinity of the ancestrida the avicularium is small and placed 

 at the level of the ascopore. The large marginal zoeceia have their avicularia 

 larger and placed in the wider part of the zooecium well below the ascopore. This 

 character is quite visible on the figure of Tuomey and Holmes and we believe that 

 it is sufficient to recognize this long-forgotten species of these American authors. 

 There are six lateral and one distal dietellae. 



Affinities. — ^This species differs from Microporella eustomata Gabb and Horn, 

 1862, and from Microporella vibraculifera Hincks, 1883, in its smaller avicularium, 

 more distant from the zooecial axis and of a more irregular position. It differs from 

 Microporella ciliata Linnaeus, 1759, in the large zooecial dimensions and its larger 

 avicularimn. 



Occurrence.— PYiocQUQ (Waccamaw marl): Waccamaw River, Horry County, 

 and Giles Bluff, Peedee River, South Carolina (Tuomey and Holmes). 



Pleisotypes. —C&t. No. 68595, U.S.N.M. 



