The Actiniae of the Plate Collectiou. 277 



diameter of 10 mm. The specimens from Coqiiimbo are practicallj^ 

 coloiiess, but tliat from Calbuco was brownisli; all the specimens 

 contain more or less browii pigment in the endoderm of the mesen- 

 teries and to a less extent in that of the tentacles. 



Structure. The mesogloea of the column wall is on the 

 average thinner than the ectoderm, but toward the margin it 

 thickens until it becomes two or three times as thick as that 

 layer and above this it diminishes again to a thin lamella (Fig. 67). 

 It is fibrous in structure and its outer surface is raised into numerous 

 ridges. The circular musculature is well developed and at the 

 margin or collar and extending a slight distance above it is a feeble 

 sphincter. This in the sm aller specimens (Fig. 67) forms a linear 

 band lying close to the endoderm, composed of two or three irregulär 

 rows of cavities in most of which only scattered muscle flbres can 

 be perceived. In the largest individual it was better developed, 

 occupying the entire thickness of the mesogloea at its upper part, 

 but it is still a weak muscle. 



The tentacles are thin-walled , the mesogloea being merely a 

 thin lamella, and the longitudinal muscles are rather weak and 

 confined to the ectoderm. The stomatodaeum is provided with 

 longitudinal ridges and of the individuals examined one possessed 

 two siphonogiyphs and another only one. 



Transverse sections were made of two individuals from CJoquimbo 

 and of each of the individuals from Calbuco, and all showed differences 

 in the arrangement of the mesenteries. In one of the Coquimbo 

 specimens they were typically hexamerous, and were arranged in 

 three cycles, those of the first cycle only being perfect. There were 

 two pairs of directives and the mesenteries of the first and second 

 eycles were provided with well-developed muscle pennons which 

 were narrow but relatively high (Fig. 68), consisting of about 

 twelve slender and somewhat branched processes. The members of 

 the third cycle lacked both pennons and mesenterial fllaments. In 

 the second Coquimbo individual there were only twenty pairs of 

 mesenteries : the first cycle contained six pairs which were all perfect 

 but included but a Single pair of directives; the second cycle was 

 represented by only four pairs of imperfect mesenteries, while the 

 third consisted of ten pairs, destitute of muscle pennons and filaments. 

 It is clear that in this individual the decamerism Starts with the 

 development of the third cycle of mesenteries and is due to the 

 failure of two pairs of the second cycle. In the Calbuco specimen 



