HISTORY OF RESEARCH. cix 



Retiolites, are cleared up by Holm's development of specimens of Stomatograptus 



(8. Tornquisti). This genus he considers to be more distinct from Retiolites than 



was previously supposed, for in Stomatograptus, in addition to the "pores," the 



form of the apertures is different. He proves that the periderm in this genus, as in 



other Graptolites, is composed of three layers ; " the outer and inner are smooth and 



without spaces, while the middle one is formed of a network of chitinous threads." 



Retiolites nassa. Another interesting form, Retiolites nassa (later made the 



type of a new genus — Gothograptus — by Freeh.), is shortly described. This form 



bears the same relation to the Retiolitidse that Glimacograptus does to the Diplo- 



graptidae. 



In 1890 Tornquist brought out the first part of his 



" Siljansomradets Graptoliter." In this paper several species 



Tornquist, „ ~ _. . . ., .. -. .. -. , 



1(C ,.,. „, , of Graptolites (some new) are carefully described and 



onjausomntdets r \ s J 



Graptoliter," i, figured. The author recites concisely his own views on the 



' Luuds Uuiv. Ars- structure of Retiolites, and discusses Tullberg's opinions on 

 skrift,' bd. xxvi. the subject. 



Description of Species. — Retiolites Geinitzianus, R. efr. 

 perlatus, and R. obesns are described and figured, and he thinks that, when better 

 material is obtained, the last species will form the type of a new genus. He 

 refers the species described by Suess (' Bohmische Graptolithen,' 1851) as R. grandis, 

 to the genus Stomatograptus. In addition, he figures Lasiograptus margaritatus, 

 Diclwg. octobrachiatus, Clonograptus robustus (allied to Gr. ramulus, Hall), 

 Tetragraptus serra, Tetrag. curvatus, Didymograptus minutns, I), gracilis, and D. 

 decens. In his description of D. minutns, he notes the long thread extending 

 from the apex of the sicula, and thinks that this might correspond more nearly to 

 the virgula in the genera Diplograptus and Monograptus. He suggests that the 

 genus Didymograptus should be made the type of a new family — the Didymo- 

 graptidae — distinct from that of the Dichograptidse on account of apparent 

 differences in the development of the branches. 



The other species described in the paper are Dicellograptus anceps, Phyllo- 

 graptus densus, Climacograptus scahtris, G. internexus, and a form which the author 

 thinks further research will prove to be a distinct species, and for which he 

 suggests a name, G. phrygionius ; Diplograptus pristis, D. truncatus, D. palmeus, a 

 new species, D. bellulus, Gephalograptus folium and G. cometa. 



In most of the specimens the sicula and its relations to the proximal theca3 are 

 carefully figured. 



1#$0. Malaise in 1890 summarised his work among the grap- 



Malaise, tolite bearing Palaeozoic rocks in Belgium, and correlated 



., ^ n . r ',; ' .. the zones with those of Britain. He recognises in Belo-ium 

 de Belgique, ' Bull. _ _ _ . . 



Acad Roy de Bel- ^ our successive chronological groups of Graptolites, viz. those 

 gique,' ser. 3, vol. xx. of the Arenig, Bala, Llandovery, and Wenlock-Ludlow, but 



