118 



BRITISH FOSSIL CRUSTACEA. 



figs. 6 & 7), and of the still nearer larval Limulus, which, in its earlier stage, has appen- 

 dages only to three of the thoracic somites. 1 



In the two annexed diagram -figures of specimens preserved in the Museum of Practical 

 Geology (figs. 37 and 38) the thoracic plate differs somewhat in form from that usually 



Fig. 38. — Thoracic plate or operculum — part of an almost entire specimen — of Slimonia acuminata (only the centre 

 of operculum drawn), showing apparently three plates overlying each other. Length of alae, 3 inches. Length 

 of median appendage, 5 inches. 



associated with Slimonia acuminata ; they deserve to be recorded, therefore, on that 

 account ; but they also appear to give evidence that they conceal beneath them one or 

 more branchigerous plates, the edges of which are seen at m, and along the lower border 

 of the lateral alae of the operculum (/,/). 



1 See ' Quart. Journ. Geol. Soc.,' 1867, vol. xxiii, p. 34. Also ' Sur le developpement des Limules,' par 

 H. Milne-Edwards, Societe Philomathique, Nov. 10th, 1838. On "The Horsefoot Crab," by the Rev. 

 S. Lockwood, Ph.D., in 'American Naturalist,' vol. iv, 1870, p. 257. Also Dr. A. S. Packard, junr., 

 ' On the Development of the " King Crab," Limulus polyphemns,' read before American Association for 

 the Advancement of Science, 1870, 'Geol. Mag.,' 1870, vol. vii, p. 491. ' Untersuchungen uber Bau 

 und Entwickelung der Arthropoden zur Embryologieund Morphologie des Litnulus polyphemus,' von Dr. Anton 

 Dohrn. Abdruck aus der ' Jenaischen Zeitschrift,'Band vi, Heft 4. (Received 30th September, 1871. — H. W.) 

 And " Further Remarks on the Relationship of the Xiphosura to the Eurypterida and to the Trilobita," by 

 H. Woodward, 'Quart. Journ. Geol. Soc.,' 1872, Part I, vol. xxviii, p. 46. 



