272 University of California Fublications in Zoology, [^ou 4 



of the plant. On inspection, these were found to be bryozoan col- 

 onies consisting- in many instances of two, three, five, or more 

 zoa?cia. Toward the extremities of the fronds larger colonies 

 were found numbering sometimes hundreds of individuals, and 

 all were identified as colonies of 31. villosa. Further examina- 

 tion showed the larva in every stage of metamorphosis, from the 

 earliest in which the shell (fig. 24a) is still fastened to the sur- 

 face upon M^hich it settles, to the latest in which zooecia were 

 formed and polypides were functioning. 



The metamorphosis of at least two other Membraniporje has 

 been observed (Ostroumoff '85), and according to Kupelwieser 

 ('06) who has recently studied Cyplionantes from many locali- 

 ties, these organisms are to be distinguished mainly in size and 

 in the denticulation of the shell. The drawing here given of our 

 western Cyplwnautes (pi. 17, fig. 24) was made from life, as were 

 also the observations recorded. They will acquaint the student 

 with the main facts of structure and habits, but for more ex- 

 haustive treatment he is referred to the literature cited in the 

 bibliography. For the sake of difi:erentiating this western form 

 from other CypJionautes it will be referred to as C. occidentalis. 



Like the familiarly known Cypltonautes compressus, C'yphon- 

 autes occidentalis (pi. 17, fig. 24) is triangular in shape and is 

 inclosed in a delicate bivalve shell. The proportion of height to 

 greatest breadth is on an average as 5 :7. For purposes of orien- 

 tation, the wide ciliated border is known as the oral, o., side, the 

 apex of the triangle, the aboral, ah. ; the side parallel with the in- 

 testine is posterior, post., and the side opposite is anterior, ant. 

 On the oral side the valves of the shell gape, permitting free com- 

 munication between the exterior and the interior. The oral 

 edges are thickened with a wide chitinous border, and still further 

 strengthened by a reddish brown chitinous rib, rb. This rib is 

 beset with a number of strong red, denticles, d., or teeth which 

 are numerous at the angles of the shell, being there set in two or 

 more alternating rows, while in the intermediate region they form 

 a single row. The apex, a., of the shell is deeply cut on the two 

 valves, and through the opening the apical tuft, ap. t., of cilia 

 protrudes. The animal within the shell differs but little from 

 C. compressus. From observation of the living organism only, 



