HISTORY OF RESEARCH. xxxv 



(A) Graptolites with many axes. Oladograpsus. 

 (a) Many-celled. ? (1) * Gl. nereitarum. 



(u) One-celled. ? Lophoclenium comosum. 



(B) Graptolites with one axis. 



(a) Many-celled. 



(1) Axis weak. Nereograpsus (Geinitz). 



(2) N.SedgwicU; (3) N. Beyrichi, .V. Mac Leayi. 



(2) Axis strong-. 



(a) Skeleton net-like. Retiolites, Barr. ; (4) B. rete (?). 

 (h) Skeleton complete. Diplograpsus. 

 (ad) Cells overlapping - . 



D. ovatus, D. folium, (5) D. palmeus, B. pristis, 1>. dentatus, 

 ((>) IK teretiusculus. 

 (bb) Cells free. 



(7) D. birastrites (= D. acuminatus), (8) D. cometa. 



(b) One-celled. Monograpsus, Geinitz. 



(1) Cells in contact. 



M. testis, (9) IT. mrfua (? ilf. Boemeri), M. colonus, (10) /If. go^i*- 

 fanw, (11) IT. Nilssoni, M. Ealli, M. SedgwicJcii, M. Eeubneri, 

 (12) M. priodon, (13) If. 5ecH, ilf. convolutus, (14) ilf. turriculatus, 

 M. proteus, M. millepeda, (15) ilf. pectinatus. 



(2) Cells free. 



-M". triangulatus, (16) iVf". peregrinus, (17) ilf. spina (?), (18) 

 .M". urceolus (?), If. Linngei, (19) Jlf. gemmatus. 



It will be seen, therefore, that Richter adopted the various genera recognised 

 by Geinitz, even including those now referred to worm burrows. Most of the 

 species of Graptolites mentioned are described and figured by Richter, and the 

 drawings are fair; but hardly any of his five new forms, viz. Retiolites rete, 

 D. birastrites, M. pectinatus, M. urceolus, and M. spina, are recognised as distinct 

 species at the present day. 



Structure. — Richter did not advance our knowledge much as regards the structure 

 of the Graptolites, but he pointed out more clearly than had previously been done 

 those characters of the cells which are of specific value, such as (1) the general form, 

 (2) the relative distance, (3) the shape, (4) the inclination, etc. Not only so, but 

 in this memoir Richter makes many original suggestions of considerable importance 

 respecting the development of the Graptolites. lie was the first to suggest that 

 the "foot" might have had some connection with the development of the 

 Graptolite ; but he does not (Miter into any details. He points out that the 

 greatest amount of growth is in the direction of length ; the circumference once 

 attained does not increase, and the lowest cells are always the shortest (except in 

 1 Note. — In this and all subsequenl papers only the species figured are numbered, 



