1910] Robe risen : Cyclostomatous Bryozoa. 253 



in the erect habit of growth of the adult form of Idmonea. Thus 

 Hincks ( '80) p. 451, says, "in their adult state the Idmoneae are 

 attached by a somewhat expanded base, the surface of which 

 is lineated or striated; but their earliest stage is, I believe, iden- 

 tical with that of Tubulipora." As an illustration of this state- 

 ment he uses /. serpens which Ilarmer has later shown to be a 

 true Tubulipora. I recognize the difficulty, as I have said before, 

 of establishing a genus on mere habit of growth, and yet I 

 hesitate to ignore the genus Idmonea since the species here 

 regarded as Idmonea is so distinctly different from those forms 

 identified as Tubulipora. Unfortunately, though having searched 

 diligently through a large quantity of material, I have not found 

 the ovicell. 



97. Idmonea calif ornica d'Orbigny. 



PI. 23, figs. 39, 40, 41. 



Idmonea calif ornica d'Orbigny, 1852, p. 732. 



Idmonea californica, Conrad, 1855, vol. vii, p. 441. 



Idmonea californica. Gabb and Horn, 1862, p. 168, pi. 21, fig. 56. 



Idmonea californica, Busk, 1875, p. 16. 



Zoarium erect, composed of numerous dichotomously branch- 

 ing stems (pi. 23, fig. 41) which in many colonies anastomose, 

 forming a rounded, reticulated mass of stems seven or more 

 centimeters high and as many broad. Branches one, two or 

 three millimeters wide, the zooecia opening on the one side only. 

 Zooecia tubular, long, extending one behind the other, so that 

 in cross-section there are three or four transverse rows of 

 openings of different sizes representing cross-sections of zooecial 

 tubes at different levels; zocecial orifices six or more in a trans- 

 verse row, sometimes directed straight forward, more often half 

 of them slightly more inclined to one side than to the other, so 

 that while a median line is not as distinct as in some species, 

 it is more or less apparent (fig. 39) ; often bent at right angles 

 to the surface, projecting prominently, the tubular projection 

 being more delicate than the ordinary zocecial wall and without 

 the pores; marked by circular lines. Oaecia? 



There is much variation in the width of the branches and 

 the mode of branching in specimens brought from different 



