32 PEOCEEBINGS OF THE GEOLOGICAL SOCIETY. [jSToV. 21, 



a third suite from the collection of John Anstice, Esq., of Madeley 

 "Wood, Wellington, Salop, together with specimens from Mr. E. J. 

 HoUier, of Dudley, and Mr. J. Earie, of Glasgow, I have, after 

 careful study, concluded that they are divisible into tiuo ivell-marhecl 

 genera : — 



(ci) Those having moveable thoracic segments and anchylosed ab- 

 dominal ones, to be included in the genus Belinurus, namely — 



1. Belinurus trUohitoides, Buckl. Coal-measures, Derry and 

 Coalbrook Dale. 



2. 7^egince, Baily (PI. I. fig. 1). Coal-measures, Ireland. 



3. arcuatus, Baily. Coal-measures, Ireland. 



4.? Dance, Meek & W. Coal-measures, Illinois, U.S. 



{h) Those in which the thoracic and abdominal segments are not 

 divided and in which the former appear to be anchylosed, to be in- 

 cluded in a new genus, for which I venture to propose, if Mr. 

 Prcstwich will allow me, the name of PrestiuicJiia ; i. e. : — 



1. Prestwichia anthrax, Prestw., sp. Coal-measures, Coalbrook 



Dale. 

 2. rotundata, Prestw., sp. (PI. I. fig. 2). Coal-measures, 



Coalbrook Dale. 



In all these six species the body consists of a head-shield, five 

 free, or anchylosed, thoracic segments, and three anchylosed abdo- 

 minal ones. 



Here, then, we have an intermediate group between Limulus 

 proper, more nearly approaching Hemiaspis &c., but having the 

 posterior (or abdominal) segments anchylosed together, and not 

 freely articulated as they appear to have been in Hemiaspis and 

 Pseudoniscus &c. Eurthermore the six free thoracic segments are 

 reduced to five in Belinurus (PI. I. fig. 2). 



In the recent Limidiis we find thirteen paired appendages, repre- 

 senting an equal number of somites, behind which there is seen one 

 or more coalesced segments destitute of appendages, to the last of 

 which the telson is articulated (see PL II. figs. 1 & 2, Ah.). 



I feel no doubt that this apodal posterior portion of the integu- 

 ment in Limidus represents the abdomen, and corresponds with the 

 three posterior coalesced segments forming that division in Beli- 

 nurus (PI. I. fig. 1, Ah.). The fossil species well illustrate the gra- 

 dual coalescence of the body-segments in this family. 



Belinurus regincB, Baily (PI. I. fig. 1) (Ann. & Mag. Nat. Hist. 

 3rd ser. (1863) vol. xi. p. 107, pi. 5), is one of the best illustrations 

 of a Crustacean with free thoracic segments, and Prestwichia rotun- 

 data (PL I. fig. 2) of one in which the segments are coalesced. 

 All the group possess, in the trilobed aspect and general facies of the 

 carapace, a strong resemblance to the Trilohitce; but this resem- 

 blance becomes still more striking when we observe their tripartite 

 division into head, thorax, and abdomen. 



Nearly all writers agree in considering the last seven somites 

 (counting the " telson" as the seventh) to be abdominal ; the only 



