NO. I S.MITHSOXIAX EXPLORATIONS, I919 I9 



this richl\" fossilifcrous rcL^ion, l)Ul lari^^c rock specimens with their 

 surfaces tinweathered are comparatively rare. I'drtunateh- for the 

 present jiiirposes. heavy freshets in the spring" of 1919 had uncovered 

 the richly fossiliferous lasers along the creek shown in figure 18, and 

 here several additional well-preserved exhihition 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 \\ith un])res- 

 sions of the branching fossil seaweed Bittliotrcphis, 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, H)\\). Dr. Bassler was detailed to ])roceed to Dayton. 

 ( )hio. in order to ])re])are for shi])ment to the Museum the largest 

 entire -\merican trilobite so far discovered. 'J'his unique specimen 

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

 tions for the llut'fnian l'onservanc\- Dam 6 miles east of Davton. 

 which forms a part of the greatest engineering ])roject ever under- 

 taken for controlling stream flow, with the exce])tion of the Assouan 

 Dam along the Nile. 1^'ollowing the destructive floods in the .Miami 

 valley in 1913. the Miami Conservancy District was organized to 

 ])revent a repetition of this disaster through the control of the 

 Miami River and its triljutaries by dams extending entireK' across 

 their valleys. This operation involving an expense of o\er tifteen 

 million dollars has been under way for three years, and w ill rc-(|uire 

 three years more for its com])letion. The view (fig. 20) show ing the 

 excavations in whic-h the trilobite was found illustrates onl\- the 

 beginning of (jne (jf these dams. This ])articular dam when com- 

 pleted, will extend a distance of a mile eiUirel\- across the ri\er vallcv. 

 Xormally the water will flow in its usual cbaniuT bul in Hood times 

 it will be retained and allowed U) esca])e gradualK . 



The trilobite which was found lying on its liack in a hard c]a\ bed 

 in the central ])art of the e.\ca\alion was unearthed b\- llu- \)\c\< of a 

 workman, wh<j believed it to be a ])etrified lintle. .Mr. Aillinr 1'.. 

 Morgan, Chief I'jigineer of llie .Miami ( onser\anr\- DiNhiet. recog- 

 ni/.t-d the true naliu"t- ami scientihc \ahie ot lln' mi i-.illed inrlle .md 

 pri'sented it to the .'Smithsonian Instilntion. where it now t'oiins a 

 most instructive and uin'(|ue i-.\hibil in the Jiall of inxeitebrate 

 pale(»iUol()g\-. The \alue ol the ■^pt'cimen i- Inilber inerea^ecl b\ lli.- 

 fact that it has become llu' type ot the new species Isotcliis hraclix- 

 rr/'/J(i//^«• described by I )r. .\ugu>t I'. I'Oersle of Dayton, ()hi(). 



