NOTES OX PALEOZOIC CRUSTACEANS 87 



nations and those pertaining to tlie preabdomen obliquely 

 grooved. In Pseudoniscus roosevelti (the New York 

 species) we find there are 10 distinct segments, one more than is 

 ascribed to this genus by Meszkowski and Schmidt, the telson 

 l)eing a spine whose base is joined directly to the ultimate joint 

 and which may be looked on as an 11th segment. B u n o d e s 

 was first described with nine segments also, but the supplement- 

 ary figures given by Schmidt on his plate 7 show it to have had 

 10, and the two genera in this regard are alike. In B u n o d e s, 

 however, pleurae on the last three segments are wanting or rep- 

 resented only by short lateral spines, while in Pseudoniscus 

 these final pleurae are very long and strongly recurved. We 

 J&nd that in Pseudoniscus the segments 1-5 have grooved 

 pleurae and the sixth and seventh are closely conjoined, so that 

 the interval between the pleurae is notably slight and the corre- 

 sponding axial parts of the segments very narrow. We do not 

 Tiow^ever regard these as coalesced into a single segment with 

 double pointed pleurae. The latter is the condition ascribed to 

 Bunodes by Schmidt, and very clearly shown in his more 

 'Complete drawings of these animals, while in the genus B e 1 i n- 

 nrus segments 7-8. are regarded as consolidated. Heretofore 

 the segments of Pseudoniscus have been regarded as 

 equally independent, and this approximation of segments 6-7 has 

 not been noted. The comparison of these structural characters 

 indicates a closer relation between these two genera than had 

 been previously conceded, without however compromising the 

 generic distinction. 



The authors who have had occasion to discuss the genetic rela- 

 tionship of these creatures, have found in their deep trilobation 

 and grooved pleurae, lines of attachment to and derivation from 

 a trilobitic stock, and Nieszkowski^ Schmidt and Woodward have 

 all agreed in looking on them as passage forms from the trilo- 

 iDites to the merostomes. I am at present inclined to the belief 

 that we have a sufficient clue to the early history of the pecu- 

 liar bodies represented by Psendoniscus, Bunodes, 

 H e m i a s p i s and Neolimulus to indicate their origin in 



