No. 3.] GEOLOGY AND MINERALOGY. 349 



longing to tlie Canadian Geological Museum, which has been 

 supposed to show remains of legs. Mr. Billings, while he has 

 suspected the organs to be legs so far as to publish on the sub- 

 ject, * has done so with reserve, saying, in his paper, " that the 

 first and all -important point to be decided, is whether or not the 

 forms exhibited on its under side, were truly what they appeared 

 to be, locomotive organs." On account of his "doubts, the speci- 

 men was submitted by him during the past year to the Geological 

 Society of London ; and for the same reason, notwithstanding the 

 corroboration there received, he oflfered to place the specimen in 

 my hands for examination and report. 



Besides giving the specimen an examination myself, I have 

 submitted it also to Mr. A. E. Verrill, Prof, of Zoology in Yale 

 College, who is well versed in the invertebrates, and to Mr. S. I 

 Smith, assistant in the same department, and excellent in crusta- 

 ceology and entomology. We have separately and together consi- 

 dered the character of the specimen, and while we have reached 

 the same conclusion, we are to be regarded as independent judges. 

 Our opinion has been submitted to Mr. Billings, and by his 

 request it is here published. 



The conclusion to which we have come is that the organs are 

 not legs, but the semi-calcified arches in the membrane of the 

 ventral surface to which the foliaceous appendages, or legs, were 

 attached. Just such arches exist in the ventral surface of the 

 Macroura, and to them the abdominal appendages are articulated. 

 This conclusion is sustained by the observation that in one 

 part of the venter three consecutive parallel arches are distinctly 

 connected by the intervening outer membrane of the venter, 

 showing that the arches were plainly in the membrane^ as only a 

 calcified portion of it, and were not members moving free above 

 it. This being the fact, it seems to set at rest the question as to 

 the legs. We should add, however, that there is good reason for 

 believing the supposed legs to have. been such arches in their con- 

 tinuing of nearly uniform width almost or quite to the lateral 

 margin of the animal ; and in the additional fact, that, although 

 curving forward in their course toward the margin, the successive 

 arches are about equidistant or parallel, a regularity of position 



• Q. J. Geol. Soc, No. 104, p. 479, 1870, with a plate giving a full- 

 sized view of the under surface of the trilohitc, a species that was over 

 four inches in length. 



