266 8. W. Ford— Embryonic Forms of Trilobites. 



■ by the researches of M. Barrande. In one instance, that of 

 Sao hirsata, he has shown that twenty such phases are passed 

 through, the earliest and simplest forms being of almost micro- 

 scopic minuteness and presenting scarcely any resemblance to 

 the individual when completely developed. These phenomena 

 have been styled by Barrande the "Metamorphoses of Trilo- 

 bites;" and in his truly magnificent work on the Trilobites of 

 Bohemia (Systeme Silurien de la Boheme, vol. i, 1852,) they 

 are fully and ably set forth and discussed. Hitherto, however, 

 no example of a truly embryonic form of trilobite, or one show- 

 ing that the animal was mainly developed after quitting the 

 egg, has been found in other than Bohemian strata; a fact 

 which, when we consider the prodigious numbers of these ani- 

 mals that existed in Paleozoic times, the care with which the 

 rocks in which they occur have been explored in many coun- 

 tries, and the profound study which their remains have received 

 at the hands of many distinguished investigators, would seem to 

 indicate that, in the greater number of species, no such forms 

 ever existed. I beg leave to submit herewith the evidence I 

 have obtained of the metamorphoses of an American trilobite, 

 the species being the Olenellus | <»plwides of 



Emmons. I shall discuss this evidence, together with certain 

 other material which I possess pertaining to this species, under 

 the following heads : 



Genus OLENELLUS Hall. 



Olenellus (Elliptocephalus) asaphoides Emm. 



I. Embryonic Forms. 



In the spring of 1868 I discovered several specimens of this 

 species in the limestone beds at Troy, showing clearly the 

 characters of Olenellus, which were afterward fully identified 

 with the Washington County form by Mr. Billings. Since 

 that time I have added to my list of specimens whenever 

 opportunity has offered. Although some of the specimens 

 obtained early in the course of my investigations appeared to 

 me somewhat rudimentary in character, yet it is only of late, 

 and after laboriously working away the partially enveloping 

 rock, that I have become fully aware of the real richness of 

 the matenal. Further researches will doubtless supply much 

 that is still desirable. 



Fig. la represents, natural size, the earliest stage of growth 

 observed, and lb the same enlarged five diameters. The speci- 

 men is nearly circular, one line in greatest width and length, 

 with a wide concave border which, toward the edge, is bent 

 upward so as to form a neat marginal rim. The glabella is 

 three-fifths the total length. It is divided into five distinct 

 lobes by four well defined furrows extending all across. The 



