A NEW HOLOTHURIAN OF THE GENUS THYONE 



COLLECTED ON THE PRESIDENTIAL 



CRUISE OF 1938 



By Elisabeth Deichmann 

 Museum of Comparative Zoology, Harvard University 



Among the echinoderms collected by Dr. Waldo L. Schmitt during 

 the Presidential cruise on the U.S.S. Houston in the summer of 1938 

 there are only two sea-cucumbers, both belonging to the same species. 

 These two individuals were collected in Magdalena Bay on the west 

 coast of Lower California. They represent a new species, which, 

 however, is closely related to a form known from tide pools in Cali- 

 fornia but, so far as our present knowledge goes, not known from 

 south of Morro Beach. 



Magdalena Bay seems to be the northern limit for the tropical 

 "Panamic" region on the western coast of Lower California, and it 

 is therefore likely that the new species will be found in other localities 

 within the "Panamic" region. On the eastern side of Lower Cali- 

 fornia the "Panamic" region reaches northward to the mouth of the 

 Rio Colorado. 



THYONE LUGUBRIS, n. sp. 



Diagnosis. — A small form, a few centimeters long, with stout feet 

 which are slightly larger and more numerous on the ventral side, 

 where the original arrangement in 3 bands often is visible ; on the 

 dorsal side some of the feet are more papilliform. Tentacles 10, the 

 2 ventral smaller than the others. Calcareous ring with distinct, 

 though fairly short, posterior prolongations on the radials ; both the 

 radials and interradials have a long anterior tooth. Stone canal small, 

 delicate, embedded in the dorsal mesentery ; head small, flattened with 

 thickened edges, free to the right. Polian vesicle single, ventrally 

 placed. 



Spicules consisting of an external layer of knobbed buttons or 

 plates with the external side covered by a reticulum. The inner layer 

 consists of regular 4-holed knobbed buttons ; the central knobs are 

 often united into a distinct handle ; some buttons are more lozenge- 

 shaped, with an accessory hole in each end. In very small- individuals 



Smithsonian Miscellaneous Collections, Vol. 98,, No. .12 



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