NO. 1323. STRUCTUBAL FEATURES OF HOMOTRYPA—BASSLER. 583 



This species is particularly interesting because of the unusual devel- 

 opment of acanthopores and mesopore?. Some specimens, however, 

 exhibit few mesopores at the surface, and these in vertical sections 

 show that as the surface is approached the mesopores close, while 

 tangential sections have a strong development of acanthopores. Other 

 specimens show at the surface few acanthopores and man}- mesopores, 

 so that some relationship seems to exist in the development of these 

 structures. Externally the acanthopores form the distinguishing 

 character, producing the sharp, knotty tubercles and the spinulose 

 surface. Under a lens the tubercles are seen to be clusters of a few 

 slightly larger cells, scarcely raised above the general surface and 

 bearing one or two large perforated acanthopores at their summits, 

 these acanthopores causing the knotty appearance. 



Occur >'''nce. — A common form in the lower part of the Richmond 

 formation at Hanover, Ohio, and less abundant in the middle division 

 at Richmond, Indiana. 



Cat. Nos. 40227-8 Harris collection, 41753-4, U.S.N.M. 



HOMOTRYPA WORTHENI (James). 

 Plate XXIV, figs. 10-14. 



Monticulipora (Monotrypa) wortheni James, Paleontologist, No. 6, 1882, p. 50; 

 No. 7, 1883, pi. I, fig. 2. 



James's description and figures of 3f. rooi'theni are scarcely sufficient 

 to recognize the species or even to place the form generically. The 

 following description is based on material identical with specimens of 

 M. wortheni in the collections of the U. S. National Museum with Mr. 

 James's label attached. 



Zoarium ramose, branches cylindrical, usuallj" about 6 mm. in diam- 

 eter and dividing frequently and rather regularly. Surface marked 

 with strong, prominent tubercles, usually 2 mm. apart. Apertures 

 polygonal, direct, rather thick walled, about nine in 2 mm. Meso- 

 pores in the tj^pical form few, although in the variet}^ described below 

 they are quite numerous. Acanthopores numerous, often inconspicu- 

 ous at the surface, but blunt when present. 



In tangential sections the striking characters are the thick walls, 

 numerous acanthopores, and wide intermural space with its dotted 

 structure. Here also communication pores are well shown. Vertical 

 sections show that the walls in the axial region are thin and rather 

 straight, but become greatl}^ thickened in the peripheral, where a 

 series of cystiphragms larger than usual is developed with a corre- 

 sponding number of diaphragms. 



The sharply tuberculated branches of this fine species readil}' dis- 

 tinguish it from associated forms. H. hasderi is quite similar exter- 

 nally, but the different internal characters, the few acanthopores, and 



