(3X) 



480 



PROCEEDIKOS OF THE GEOLOGICAL SOCIETY. [May 11, 



from the spaco botwren tlic two lobop of the hj'pofitoma, whero wo 

 must .suj)poso tho mouth to b" situated, baolswards along the median 

 line to tlie pygidium. Tliis coiicsponds in position to the sternum 

 of tlie ordinary orustaoea. The U'gs are arranged in eight pairsr. tho 

 l)aseH of eacJi ]»air being situated exactly under one of the eight seg- 

 ments of the thorax, and at the sides of the sternal groove. 



The legs of the tirsi pair are better- preserved than the others. 

 They curve forAvardis and eaii lie traeed to a point nearly under the 

 outer edge of the eye, or, rather, between the eye and the outsidi' »i 

 tho head. The otlier seven pairs follow at the average distanec of 

 two and a half lines from eaeh other. The eight pairs thus occupy 

 about twenty lines of tlio h ngth of the ventral surface. This is 

 exactly the length of the thorax, measured on the upperside. This 

 trilobite has always eigbt segments in the thorax ; and there is thus 

 on the underside one pair of ai>p<'ndag(!8 to vAich segnuint. Although 

 some of them are veiy imperfect, and the portions tliat remain are 

 somewhat displaced, with a little study of tho specimen it can be 

 seen that they all curve forwards, and arc thus, most probably, am- 

 bulatory rather than natatory h'gs. 



There appear to be several joints in each of these appendages; but 

 the exact number cannot be made out. On the left side, the first 

 four legs show very clearly that there are at least two, one at five 

 lines from the side of the groove, and another about three lines fur- 

 ther out. The position of eaeh of these is indicated by a small protu- 

 berance (PI. XXXI. fig. !,)()• On the right side the preserved jtortions 

 of the legs are longer, and thus indicate a greater number of arti- 

 culations, although they canrot be distinctly seen. I think that 

 each leg consist(Hl of at least four or five articuhitions, 



On the pygidium there are three small ovate tubercles, arranged 

 in a line, that i ""em to be organic (fig. l,d); and if they are so, they 

 are, perhaps, the processes to which respiratory feet Avere attached. 



The length of the specimen is four and a half inches, and tho 

 width two and a half inches. On a side view the height of the 

 head just behind the eye j is nine lines, and at the middh- of tho 

 thorax about seven lines. The depth of the internal cavity at the 

 back part of tho head is seven Hues, and at the last segment of tho 

 thorax four lines. The plane in which the legs are situated is 

 therefore not so low down as the extremities of the pleune. The 

 visceral cavity is thus about one-third less than the whole bulk of 

 the animal (Vl XXX II. fig. 1). 



The above is all that I desire to say at present concerning this 

 remarkable .spt^inien. The first and all-important point to be de- 

 cided is, whether or not the forms exhibited on its underside are 

 truly, what thoy appear to be, locomotive organs. If this question 

 be decided in the atfirmative, it will then remain for Oarcinologists 

 and othi-rs to homologize them Avith the limbs of existing Crustacea. 

 It is scarcely necessary to remark, in this place, that, in view of 

 the great zoologieal questions that are at present being discussed, 

 the correct determination of the affinities of the Trilobit(»8 is of ex- 

 traordinary importance. 



