180 



BULLETIN 11, UKTITED STATES NATIONAL MUSEUM. 



smooth; maculae of slightly larger zocEcia at regular intervals but 

 indistinctly visible; zocecial aperture small, polygonal, nine to ten 

 in 2 mm., with rather thick, minutely granular walls bearing acan- 

 thopores of some size, one or two to a zooecium; mesopores wanting. 



The internal characters agree in all respects with typical species 

 of the genus. The minutely granulose walls and distinctly granulose 

 acanthopores, and the absence of mesopores, are well brought out 

 in tangential sections, while vertical sections show the usual cysti- 

 phragms forming either a single or double row in each zooecial tube. 



It is possible that more material may show the incrusting expan- 

 sions upon which the variety is founded to be nothing but the base 

 of ramose zoaria. In this event the varietal name is almost useless, 



Fig. 93. — MONTICULIPOEA AEBOEEA BISPINULATA. O, ONE OF THE TTPE-SPECIMENS, NATURAL SIZE, 

 INCEUSTING A BEACHIOPOD FRAGMENT; b AND C, TANGENTIAL SECTION, X20, AND A PORTION, X30, SHOW- 

 ING THE TWO SETS OF GRANULOSE ACANTHOPORES AND THE WALL STRUCTURE; d AND 6, A VERTICAI, 

 SECTION, X20 AND X30, WITH THE CTSTIPHEAGMS LINING BOTH SIDES OF THE TUBES. WASSALEM BEDS 

 (D3), UXNOEM AND GUT SACK, ESTHONIA. 



since in practically every other feature the structure is precisely as 

 in M. arbor ea Ulrich. It is true that the granules of the walls in the 

 variety are so large that they have the appearance of acanthopores, 

 thus with the real acanthopores giving the idea of two sets of these 

 structures. Upon this character and the incrusting growth I have 

 distinguished the Russian specimens as a variety. 



Occurrence. — Monticulipora arhorea is a ramose form described by 

 Ulrich from the Clitambonites beds of the Lower Trenton in Min- 

 nesota and Iowa. The species reappears in higher beds of the 

 Trenton formation in Kentucky. Variety hispinulata is represented 

 by two incomplete specimens from the Wassalem beds (D3) at 

 Uxnorm, near Reval, and at Gut Sack, Esthonia. 



Cotypes.—Csit. Nos. 57268, 57269, U.S.N.M. 



British Museum, thin section of a type-specimen. 



