Stereomastis Sp. Bate. 



Stereomastis C. Spence Bate, Report on the Challenger Macrura, 1888, p. 154. 

 Polyclieles A. Alcock, A descriptive Catalogue of the Indian Deep-Sea Crustacea, Calcutta 

 1901, p. 166. 



In this genus the lateral margins of the carapace are constantly armed with less than 

 20 spines, the median dorsal ridge is smooth and carries a definite number of 4 to 7 spines 

 and there are invariably two spines at the outer angles of the anterior border of i st abdominal 

 somite, except only in Stereom. cerata (Alcock). The epipod of the external maxillipeds is 

 rudimentary, while those of the thoracic legs are membranous expansions of the base of the 

 podobranchs. 



The genus Stereomastis contains at present 10 species and 1 variety : just as is the 

 case with the genus Polyc/icles, most species inhabit the Indopacific. Like Polycheles typhlops 

 Heller in the genus Polycheles, it is in this genus Stereom. sculpta (S. I. Smith) that presents 

 a very extended geographical distribution : this species, indeed, occurs from Nova Scotia along 

 the east coast of the United States to the West-Indies ; it has been observed in the eastern 

 Atlantic, in the Gulf of Gascony and in the western half of the Mediterranean, furthermore 

 at Cape Natal and in the Arabian Sea, while it has been secured by the "Siboga" even in 

 the Bali Sea and at the entrance of the Gulf of Boni. A variety pacifica Fax. is found in the 

 Gulf of Panama and off the west coast of Mexico. Still another species of Stereomastis occurs 

 along the east coast of the United States and specimens from the Gulf of Panama hardly 

 dilier from the type form : this species is Stereom. nana (S. I. Smith), which has wrongly 

 been regarded as a dwarf deep-water variety of Stereom. sculpta. Near Magellan Strait and 

 off the south western coast of South America Stereom. Suhmi was discovered by the "Chal- 

 lenger", while Skrconi. Grimaldii (Bouv.) occurs on the coast of Senegal: the latter species, 

 however, has quite recently been captured off the south-west coast of Ireland and is regarded 

 by Selbie as a variety of Stercom. nana (S. I. Smith). The 6 other species are all distributed 

 throughout the Indopacific. The Indian Ocean, north of the Equator, is inhabited by Stereom. 

 andamanensis (Alcock), cerata (Alcock) and p/iosp/iorus (Alcock); the first and the third of these 

 species as also Stereom. trispinosa (de Man), a new form discovered by the Siboga expedition, 

 are found in the Indian Archipelago, while Stereom. phosphorus has moreover also been observed 

 off the Hawaiian Islands. Stereom. auriculata (Sp. Bate) is known from near the Fiji Islands, the 

 last species, finally, Stereom. Helleri (Sp. Bate), was taken north of New Guinea. 



The greatest depth at which a species of this genus has been observed, was 191 7 

 fathoms, at which depth Stereom. nana has been secured off the east coast of the United States. 



Key to the species obtained by this expedition. 



a. Median ridge of the gastric region carrying behind the two rostral 

 teeth three spines, the penultimate of which is doublé; 

 median carinae of the i st until and inclusive the 5 th terga 

 culminating anteriorly in a spine sculpta (S. I. Smith) 



