's RIJKS MUSEUM VAN NATUURLIJKE HISTORIE — LEIDEN. 15 



III. — PALLENOPSIS AND RIGONA, WITH DESCRIPTION OF 

 A NEW SPECIES. 



BY J. C. C. LOMAN, AMSTERDAM. (WITH 6 TEXTFIGURES). 



Pallenopsis is one of the earliest-known Pycnogonids, yet it also may 

 boast of being well-nigh the most misunderstood. Its name and ex- 

 haustive characteristics were published not until 1880 by Wilson, but 

 as early as 1804 Latreille gave an account of an animal by the name 

 of Phoxichilus phalangioïdes, which lately proved to be a true Palle- 

 nopsis. For this original description I beg to refer to my newly published 

 article. l ) 



Wilson has given the following diagnosis of his new genus: 



„Body slender as in Phoxichilidium, segmented. Rostrum cylindrical. 

 Abdomen slender, simple. Antennae with four joints, large and chelate. 

 Palpi rudimentary, composed of a single joint. Accessory leg present in 

 both sexes, ten-jointed. Legs slender, dactylus with auxiliary claws. Two 

 very unequal pairs of large ocelli." 



He further mentions the peculiar glandular duct near the middle 

 of the fourth joint of the legs in the male which he supposes to be 

 perhaps of generic significance. 



The number of known species amounts to more than thirty, which 

 I have enumerated in the following table. They have been arranged after 

 the depths they were caught in. Moreover I have given in the list some 

 characteristics of the animals, clearly showing the most important special 

 differences. 



Depth. Most species belong to the genuine deepsea-forms, however 

 not a few are found in shallow water ; of some others, the depth they 

 live in, is unknown. Moreover the same species sometimes was met with 

 both in the abyss and in much smaller depths. In general the probabilities 

 are that deep-sea-species at the same time often occur in shallow water. 

 In the list only the greatest depth is quoted. 



Segmentation. Most of the species have distinct segments, but 

 there are some with a short and rigid trunk, all segments having grown 

 together, admitting of no movement. Still others stand between those extre- 

 mes. The segmentation of P. patagonica (or of its synonyms) is some- 

 times perfect, sometimes less distinct. The cause of these differences is 



1) Loman, Les Pycnogouides et les règles [de la nomenclature zoologique, in; Tijdschr. Ned. 

 Dierk. Vereen. (2), 14, 1915, p. 187. 



