American Palaeozoic Bryozoa. 



233 



similis, M. parasitica, and M. wetherbyi, and four others, which for 

 the present must remain unpublished. 



Under my definition of the genus Monticulipora, on p. 153 of this 

 volume, I reduced Hall's Trematopora to the rank of a subgenus. 

 That reference I now wish to retract, my opinion of Trematopora 

 having undergone a change, since making the discovery that I had 

 committed an unfortunate error, by transposing the labels on the sec- 

 tions cut from two, externally similar, though internally widely differ- 

 ent species of biyozoans. About one year ago, Prof. R. P. Whitfield, 

 the curator of Geology at the American Museum of Natural History, 

 New York, very kindly presented me with an authentic fragment of 

 Trematopora tuberculosa, Hall, which, being the first species described 

 under the genus, Trematopora must therefore be regarded as its type. 

 Of this fragment I made three sections, a longitudinal, a transverse, 

 and one tangential. At the same time I also prepared three similar 

 sections from an example of the species I subsequently described under 

 the name of Homotrypa obliqua, n. sp. In labeling the sections of 

 these two forms, I erroneously wrote Trematopora tuberculosa on the 

 slides which I know contained sections cut from the fragment of H. 

 obliqua. After an examination, I came to the conclusion that Trema- 

 topora tuberculosa could not be considered to differ generjcally from 

 the species described further on under the name of Homotrypa curvata. 

 Although I now regard the latter as differing in a generic sense from 

 Monticulipora, D'Orb. (as restricted by me), two months ago I was 

 uncertain, and preferred to arrange Trematopora as a subgenus under 

 Monticulipora, rather than either to give the name the rank of a dis- 

 tinct genus, or to discard it altogether. The mistake was discovered 

 after making another series of sections of the species obliqua, which 

 of course were found to be identical with those at first labeled Tre- 

 matopora tuberculosa. To insure certainty, I begged Prof. James 

 Hall, the accomplished palaeontologist of Albany, New York, to send 

 me a fragment of his T. tuberculosa, which I might consider typical 

 and authentic. He obligingl}" sent me two specimens, from which I 

 prepared a series of sections that agreed in all respects with those 

 formed} 7 made and supposed to belong to obliqua. Having now found 

 that my definition of Trematopora (ante p. 153) does not apply to 

 the t}-pe species of that genus, and having also come to the conclusion 

 that the group of species which I had intended to arrange under that 

 name, is generical^ differentiated from Monticulipora, it becomes 

 necessary to propose a new genus for their reception. I therefore beg 



