184 A. S. PACKARD, JR., ON THE 



resembled those of Limulus, and like them have been surrounded by a tough, thick chorion, 

 as Barrande supposes must have been the case. He states that these eggs occurred in the 

 form of black spherules, some two-thirds, and others four or six millimetres in diameter,^ 

 mingled in the same beds with fragments of Trilobites. After giving in detail his reasons 

 for suj^posing them to be eggs, he says, " as regards their size, the spheroids in question 

 could have been the eggs of Trilobites, because the smaller ones have exactly the same 

 diameter as the first age of Sao hirsuta, namely : two-thirds of a mm. The greater diam- 

 eter of the other spheroids (two to five mm.) is in accordance with the size of the Trilobites 

 among which they have been found, as Acidaspis Verneuill and Clieirurus Qiienstedti." 



As regards the close resemblances between the adult Limulus and Trilobites, the facts 

 presented by Mr. Billings^ have enabled that able palaeontologist to make the comparison 

 between the forms of the two grou2DS a very close one. His discovery of a specimen of 

 Asaphus ptlatycephalus preserved on the under side, so as to present indications of what he, 

 with some reserve, considers as eight pairs of five-jointed legs, instead of the hypothetical 

 phyllopodous feet of Burmeister and other authors, if it should be confirmed, at once places 

 them in the closest relation with the Merostomata. 



The specimen here alluded to was submitted to the members of the Geological Society 

 of London, and Mr. H. Woodward pronounced in favor of Mr. Billings's views. On the 

 other hand. Prof. J. D. Dana, to whom Mr. Billings also sent the specimen for inspection, 

 concludes (Amer. Jonrn. Sc, May, 1871, p. 320) with Messrs. Verrill and Smith, 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 



' The eggs of Limulus are a little less than two millimetres the space between the two lobes of the hypostoma, where 



in diameter. we must suppose the mouth to be situated, backwards along 



the median line to the pygidium. This corresponds in posi- 



^Mr. Billings thus describes the specimen which good for- tion to the sternum of the ordinary Crustacea. The legs are 



tune had placed in such good hands, and of which he read a arranged in eight pairs, the bases of each pair being situated 



short notice before the Natural History Society of Montreal, exactly under one of the eight segments of the thorax, and 



in 1864. at the sides of the sternal groove. 



"This specimen was collected in the Trenton Limestone, "The legs of the first pair are better preserved than the 



at the City of Ottawa, about ten years ago. When discov- others. They curve forwards, and can be traced to a point 



ered it was lying flat upon a thin slab of limestone, and well nearly under the outer edge of the eye, or rather between 



preserved with the exception of the eyes, which seem to the eye and the outside of the head. The other seven pairs 



have been forced inwards by pressure fi-om above. It was follow at the average distance of two and a half lines from 



also divided into two pieces by a fissure wliich extended each other. Tlie eiglit pairs thus occupy about twenty lines 



diagonally across, from the first segment of the thorax on of the length of the ventral surface. This is exactly the 



the left side to the fifth segment on the right. length of the thorax, measured on the upper side. This 



"It remained in the Museum for several years without at- trilobite has always eight segments in the thorax, and there 



tracting particular attention, until one day, observing that is thus on the under side one pair of appendages to each 



the part in front of the fissure was somewhat loosely segment. Although some of them are very imperfect, and 



attached, I removed it, and was surprised at finding, on the the portions that remain are somewhat displaced, with a 



under side, not only the hypostoma in place but also what little study of the specimen it can be seen that they all 



appeared to be some of the legs of the animal. As the part curve forwards, and are thus, most probably, ambulatory 



beliind the fissure was more firmly attached to the stone, I rather than natatory legs. 



had it cut across just behind the eighth segment by the lap- "There appear to be several joints in each of those appcnd- 



idary of the Survey. Tlie remainder of the thorax was then ages, but the exact number cannot be made out. On the 



easily split off. The pygidium came off with difficulty, and lefl side, the first four legs show very clearly that there are 



in two pieces. All the pieces were then fastened together, at least two, one at five lines from the side of the groove, 



and we thus obtained two specimens, one of which shows the and another about three lines further out. The position of 



under side of the trilobite and the other its impression on each of these is indicated by a small protuberance (PI. I, 



the stone. fig. 1, n). On the right side the preserved portions of the 



"On the under side a broad, shallow groove extends fi-om legs are longer, and thus indicate a greater number of articu- 



