4 PROCEEDINGS OF THE NATIONAL MUSEUM vol.73 



my material includes a number of specimens which undoubtedly 

 belcmg to the same species and a diagnosis of this species is found 

 in the following pages. The study of its anatomy proves that it 

 belongs to the genus Loxothylacus. 



In the West Indian region, however, more than one species of 

 Sacculinidae occur. Besides that described by Gissler, this family 

 is represented by many other species, as I demonstrated a few years 

 ago when I examined the material collected by Dr. Van der Horst 

 at Curagao (Boschma, 1925). Three specimens of Sacculina were 

 represented in this collection, each of which constituted the type 

 specimen of a new species. 



Although there are a great number of West Indian species of 

 Sacculinidae, only two seem to occur as conmaon forms. One of 

 these is Gissler's species, the other, which is described in the present 

 paper under the name Drepam^orchis occidentalism has not been 

 recorded before. It is an interesting fact that each of these species 

 is found on several species of crabs, but each infests a definite group 

 of systematically related hosts. Drepanorchis occidentalis lives on 

 crabs of the family Majidae, whereas Loxothylacus panopaei is 

 known as a parasite of Panopeus and nearly allied genera, all of 

 which are representatives of the family Xanthidae. Consequently 

 just as in European species the Sacculinidae of the West Indian 

 region are restricted to definite families of crabs within which these 

 two common parasites infest several different species. 



The descriptions of the two species that follow are entirely based 

 on the material of the United States National Museum, in which 

 both are represented by a number of specimens. 



DREPANORCHIS OCCIDENTALIS, new epecies 



Type.— C2it. No. 60608, U.S.N.M., on Mithrax forceps (A. M.-E.), 

 " Fish Hawk " Sta. 7153. Deadman's Bay, west coast of Florida. 



The shape of the animals is roundish or somewhat irregular, often 

 with more or less well-marked angular tips. (Fig. 1.) The size is 

 variable, some specimens have a greater diameter of 4 mm. or less, 

 whilst others are much larger. The largest specimen in the collec- 

 tion (fig. Ic, d) measures 11.5 mm. from the dorsal to the ventral 

 surface (the diameter at right angles with the axis through the 

 mantle opening and the stalk). As in other species of Sacculinidae 

 the size of the parasites depends at least partially on the size of their 

 hosts : The larger specimens are found on crabs belonging to species 

 which may attain a comparatively large size. 



The mantle opening, which lies approximately opposite the stalk, 

 is rather wide. It is often surrounded by a wall-shaped projection of 

 the mantle, which may form a tubelike expansion. 



