SECONDARY AND TERTIARY FORMATIONS OF NORTH AMERICA. 169 



lules without any definite arrangement. Cellules usually separated laterally by a 

 faint depression, with their surfaces transversely striated ; anterior end abruptly bent 

 forwards, so as to stand nearly at a right angle with the branch. Opening circular, 

 not unfrequently closed partially or wholly by a testaceous plate, placed just inside 

 the margin of the mouth. Back of the colony transversely and irregularly striate, 

 often marked by faint longitudinal lines. 



Locality. — Santa Barbara, Cal. Miocene. 



This species is described from Mr. Conrad's original specimens. It is readily recog- 

 nized by the flattened branches, prominent cellules, with the spaces between their 

 mouths depressed, and the apparently entire absence of anastomosation. We have 

 examined a large number of specimens without finding any traces of it. There is 

 considerable variation in the width of the branches as shown by figures a and b. In 

 the narrow form the cellules are usually arranged with much less regularity. This is 

 so striking at times that we were at first inclined to consider them two species. Fur- 

 ther examination, however, satisfied us of their specific identity. 



SEMITUBIGERA. 



Colony in a free plate, meandriform or tubular; cellules on one side; external, when 

 tubular ; arranged in rows, usually with more than one series of cellules to a row. 

 Back, or insides of tubes, covered by an epithelium. This genus, as characterized by 

 d'Orbigny, always has two or more rows of cellules in each series. The species before 

 us shows, occasionally, two cellules abreast of each other, but this is of very rare oc- 

 currence. We do not feel warranted in separating it on that ground, and if we did, 

 would either have to place it with Idmonea, with which genus it seems less nearly 

 related than with the present one, or form a new genus to receive it ; neither of which 

 alternatives do we consider necessary. It occurs in plates, often like Semilubigera la- 

 mellosa, figured by d'Orbigny, and since the biserial arrangement does sometimes occur, 

 though very rarely, we place it here. Were we to consider it uniserial, on account of 

 the preponderance of that character, it is certainly as distinct from Idmonea as Semi- 

 escltara is from Retepora. 



S. tuba, n. s., fig. 57. — Colony usually in short, cylindrical or compressed and va- 

 riously carinate tubes, sometimes in tortuous plates. Cellules on one side, externally, 

 when tubular, arranged in rows having a transverse or radiating tendency, rows anas- 

 tomosing, bifurcating or ending abruptly, rarely entire. Cellules, as remarked above, 

 usually uniserial ; rarely, for a distance of two or three cellules, biserial. Bows nar- 

 row, prominent, ending abruptly at the margin. Back and inside of tubes covered 

 with a heavy epithelium, longitudinally striate and transversely corrugate. 



Locality. — Santa Barbara, Cal. Miocene. 



