30 INTRODUCTION. 



Ulricli has divided the Bryozoa which are tubular and asetose 

 into two groups the Cyclostomata and the Trepostomata. So 

 great is the difference in structure amongst the Bryozoa included 

 in these two divisions, that Ulrich's proposal seems to me wise. 

 In his important monograph on the Paleozoic Bryozoa of Illinois, 1 

 he has given general descriptions of these divisions rather than 

 definite diagnoses, and he has included among the Trepostomata 

 forms which I prefer to leave with the Cyclostomata. The fol- 

 lowing diagnoses show the sense in which I accept Ulrich's new 

 order. 



Cyclostomata. Zooecia tubular and simple in structure. Aper- 

 tures terminal (and rarely subterminal) ; inoperculate. Appen- 

 dicular organs, mesopores, and acanthopores absent. Dactylethra3 

 and cancelli may be present. 



Trepostomata. Zocecia consisting of prismatic or cylindrical 

 tubes, generally forming massive zoaria or thick sheets. Aper- 

 tures always terminal ; crowded. Zooecia divided into a proximal, 

 immature, thin-walled part, which is simple in structure ; and a 

 distal, mature part, of which the walls are thick and complex, 

 and in which the zooecia are crossed by diaphragms. Mesopores 

 and acanthopores often present ; no avicularia or vibracularia, but 

 spines may occur. 



The formation by TJlrieh of this group of Trepostomata consider- 

 ably simplifies the classification of the old order, the Cyclostomata. 

 The step was foreshadowed by Mr. "Waters, who in 1887 proposed 

 to divide the Cyclostomata into the Parallelata and the Hectangu- 

 lata. Had he formally diagnosed these groups, his names would 

 have had priority over Ulrich's ; but, as it is, it would be unfair to 

 the American author to reject the terms which he has based on 

 careful descriptions and elaborate microscopical investigations, for 

 others tentatively advanced. 



2. Previous Classifications of the Cyclostomata. I have no in- 

 tention of attempting here to discuss the respective value of the 

 classifications of the Cyclostomata which we owe to D'Orbigny 

 (1851), Hagenow (1851), Busk (1859 and 1875), Smitt (1865), 

 Hincks (1880), MacGillivray (1887), Pergens and Meunier (1887), 

 Waters (1885), Jullien (1883), Novak (1877), or Marsson 



Geol. SUIT. Illinois, vol. viii. sect. vii. 1890. 



