208 



BUUi-ETIN" "11, UNITED STATES NATIONAL MUSEUM. 



. As understood at tlie present time, this genus has abundant repre- 

 sentatives in the southern Atlantic faunas of Upper Ordovician time, 

 but, with a single exception, no species are known in other Ordovician 

 formations. The exception is the Leptotrypa hexagonalis Ulrich, 

 known in America only in the Platteville limestone of Wisconsin 

 and Minnesota, but represented in the Kuckers shale (C2) of Esthonia 

 by numerous specimens. 



LEPTOTRYPA HEXAGONALIS TJlricli. 



Text figs. 112-114. 



Leptotrypa Tiexagonalis Ulrich, Geol. Surv. lUinois, vol. 8, 1890, p. 455, pi. 36, 



figs. 6, 6 a; Geol. and Nat. Hist. Surv. Minnesota, vol. 3,pt. 1, 1893, p. 317. 



Original description. — Zoarinm forming parasitic expansions less than 1 mm. in 



thickness, spread upon Orthoceras and Eyolithes. Surface emooth. Clusters of cell 





'?!j^.Jr2*' 



Fig. 112.— Leptotrypa hexagonaus. a, the original type of the species, natural size, inckusting 

 A Htolithes; &, surface of the same, X12. Middle Ordovician (Platteville) limestone, Min- 

 eral Point, Wisconsin. (After Ulrich.) c, a fragment of limestone "with a Htolithes in- 

 crusted BY this delicate betozoan. Kuckees shale (C2), Baron Toll's estate, Esthonia. 



apertures of almost twice the usual size are arranged in diagonally intersecting rows; 

 these clusters are about 3 mm. apart, measm'ing from center to center. Zooecia regu- 

 larly hexagonal in shape, sometimes a little elongated, seven, measuring longitudinally, 

 almost nine, diagonally, in 2 mm.; diameter of the smaller 0.2 of the larger 0.35 mm. 

 Acanthopores prominent on the surface when well preserved. 



The usual occurrence of this species in America is as a delicate, 

 lace-like expansion upon shells of the pteropod EyolitJies laconi Whit- 

 field. The occurrence in the Kuckers shale is identical, even to a 

 great resemblance of the incrusted pteropod to E. haconi, although 

 this shell is probably the form described by Eichwald as Hyolithes 

 striatus. The internal structure of Leptotrypa Tiexagonalis has never 

 been figured and I am taking this opportunity of presenting thin sec- 

 tions of the type, mainly for comparison with similar sections of the 

 Russian form. Comparison of figures 113 and 114 will show prac- 

 tical identity of structure in the corresponding parts of the sections. 

 The size, shape, and thinness of the cells are especially similar. The 

 Russian specimens, however, exhibit an interesting feature which 

 has not been observed in the American examples. This is the occur- 

 rence exclusively of small, thick-walled, closely tabulated mesopore- 



