NO. I SMITHSONIAN EXPLORATIONS, I919 I9 



this richly fossiHferous region, but large rock specimens with their 

 surfaces unweathered are comparatively rare. Fortunately for the 

 present purposes, heavy freshets in the spring of 1919 had uncovered 

 the richly fossiHferous layers along the creek shown in figure 18, and 

 here several additional well-preserved exhibition slabs were secured 

 and transported to the freight station by the rail route mentioned be- 

 fore. One of these specimens, a slab several feet in length and width, 

 is worthy of special mention, as its surface is crowded with nnpres- 

 sions of the branching fossil seaweed Bittlwtrcphis, and with excel- 

 lent examples of the dumbbell seaweed Arthraria. The discovery 

 of this specimen was most fortunate as a large slab containing an 

 assemblage of these ancient plant remains has long been needed for 

 the exhibition series of fossil plants. 



In October, 1919, Dr. Bassler was detailed to proceed to Dayton, 

 Ohio, in order to prepare for shipment to the Museum the largest 

 entire American trilobite so far discovered. This unique specimen 

 (fig. 19) was discovered in the Richmond formation in the excava- 

 tions for the Hufi:'man Conservancy Dam 6 miles east of Dayton, 

 which forms a part of the greatest engineering project ever under- 

 taken for controlhng stream flow, with the exception of the Assouan 

 Dam along the Nile. Following the destructive floods in the Miami 

 valley in 1913, the Miami Conservancy District was organized to 

 prevent a repetition of this disaster through the control of the 

 Miami River and its tributaries by dams extending entirely across 

 their valleys. This operation involving an expense of over fifteen 

 million dollars has been under way for three years, and will require 

 three years more for its completion. The view (fig. 20) showing the 

 excavations in which the trilobite was found illustrates only the 

 beginning of one of these dams. This particular dam when com- 

 pleted, will extend a distance of a mile entirely across the river valley. 

 Normally the water will flow in its usual channel, but in flood times 

 it will be retained and allowed to escape gradually. 



The trilobite which was found lying on its back in a hard clay bed 

 in the central part of the excavation was unearthed by the pick of a 

 workman, who believed it to be a petrified turtle. ]\Ir. Arthur E. 

 Morgan, Chief Engineer of the Miami Conservancy District, recog- 

 nized the true nature and scientific value of the so-called turtle and 

 presented it to the Smithsonian Institution, where it now forms a 

 most instructive and unique exhibit in the hall of invertebrate 

 paleontology. The value of the specimen is further increased by the 

 fact that it has become the type of the new species Isotchts brachy- 

 cephalus described by Dr. August F. Foerste of Dayton, Ohio. 



