ACTINIANS OF GULF OF CALIFORNIA— CARLGREN 



431 



?}-mastigophors or amastigophors) ; those of the tentacles partly 

 14.8-19 by 3-3.5 /., partly 24.7-31 by 3.5-4.2 ^ (often somewhat 

 curved, microbasic ja-mastigophors ?) those of the actinopharynx 

 23.3-31 by 2.8-4 fi (basitrichs) ; those of the filaments 11.3-18.3 

 by 4.2-6.3 yu, (piriform, microbasic p-mastigophors) ; those of the 

 acontia partly 46.5-55 by 5.6-6.3 /a (probably microbasic amasti- 

 gophors), partly 26.8-32 by 2.8 fi (basitrichs or microbasic &-mas- 

 tigophors). All nematocysts are unexploded and therefore the 

 type of nematocyst is usually difficult to decide. 



Figure 81. — a, Isometridium rickettsi, new species, longitudinal section of capituluna 

 and fold {Sp, sphincter; Tn, f^nacle; Rm, radial muscles;; Fl, fold; Or, inner part 

 of oral disc) ; b, I. rickettsi, part of sphincter in the scapus. c, Anthotho'e 

 panamensis (Verrill) ? sphincter, d, Botruanthus benedeni (Torrey and Kleeber- 

 ger), cnidorages {Cn) on a branched craspedoneme. 



Measurements. — Diameter of pedal disc and height of the 

 column 11 cm., corona up to 12 cm., length of tentacle 0.5-0.6 cm. 



Holotyve.—U.^.^M. No. 49458, Guaymas, Mexico, April 9, 

 1940. 



Remarks. — The appearance of this very interesting type (pi. 14, 

 fig. 3) resembles that of Metridium, but its organization is quite 

 different from that of this genus. The scapus is smooth but very 

 wrinkled, probably owing to strong contraction. The part of the 

 sphincter situated in the scapus is rather short, occupies at most 

 about two-thirds of the thickness of the mesogloea, and is wholly 

 separated from the endodermal muscles of the column. It is dis- 

 tinctly transversely stratified and the larger muscle meshes are 

 divided into numerous smaller ones (fig. 81, b). It diminishes 



