BRYOZOA. 231 



Homotrypella (?) ovata.l 



in 3 mm. Apertures oblique in some of the young examples, nearly or quite direct 

 in the others ; in the latter the numerous small acanthopores cause more or less 

 irregularity in the outline of the apertures. Mesopores of unequal sizes, irregular in 

 arrangement, scarcely more numerous than the zooecia, from which it is sometimes 

 difficult to distinguish some of the larger ones. 



Internal characters: These are but illy preserved in the two sets of sections 

 prepared, and all the characters shown in them are brought out in figs. 10, 11 and 

 12, on plate XXVI. Four vertical sections fail to exhibit any positive evidence of 

 either diaphragms or cystiphragms, the tubes appearing as open throughout. This 

 condition, however, seems unnatural and probably due to imperfect preservation. 

 There should be some transverse partitions in the tubes, though these, especially 

 the cystiphragmsj must have been comparatively few in this species. A similar 

 absence of diaphragms, in this case obviously due to imperfection, is sometimes met 

 with in sections of H. gracilis (Chcetetes gracilis Nicholson), of the Hudson River rocks, 

 which the present species is believed to resemble more than any other. And yet I 

 am satisfied that, when sufficiently good material can be studied, the internal char- 

 acters will prove equally as near to those of the associated H. instabilis, with which I 

 had at first confounded it. 



Formation and locality. Rather rare in the middle third of the Trenton shales, at Minneapolis and 

 St. Paul, Minnesota. 



HOMOTRYPELLA (?) OVATA, n. sp. 



PLATE XVIII, FIGS. 23-30. 



Zoarium small, ramose, branches generally compressed, sometimes subcylin- 

 drical, varying between 2 and 5 mm. in diameter or width, dividing at unequal inter- 

 vals. Surface without monticules, but exhibiting at intervals of 2 or 3 mm. clusters 

 of cells of larger size and more widely separated than the average. Zocecial apertures 

 rounded, commonly a little oblique, oval and enclosed by a thin but slightly elevated 

 peristome on which a single small acanthopore is in most cases to be detected, 

 though generally with some difficulty. Interspaces depressed, with the mouths of 

 the rather large mesopores occupying them, closed or open, probably according 

 to the state of preservation. The zooscial rims are nearly always in contact with 

 each other at limited points, yet many individual zooecia, especially of those in the 

 clusters mentioned, may be completely separated from their neighbors by mesopores. 

 In some specimens, preserved unusually well, the interspaces are granulose, the 

 granules seeming to form rows on the walls separating the mesopores. Long diam- 

 eter of average zocecium 0.17 mm.; some of the largest in the clusters 0.25 to 0.30 

 mm.; ten to twelve in 3 mm. 



