50 THE VOYAGE OF H.M.S. CHALLENGER. 



The only specimen brought home by the Challenger is attached to the spine of an 

 Echinid, and was dredged in the Atlantic, — near the Azores, at Station 73, June 30, 

 1873; hit, 38° 30' N., long. 31° 14' W. ; depth, 1000 fathoms; bottom temperature, 

 3°7 C; bottom, Globigerina ooze. 



Observations. — Dichelaspis sessilis is the first instance of a Dichelaspis dredged 

 up from a considerable depth. Two other species, however (Dichelaspis loivei and 

 Dichelaspis iranvickii), were found attached to crabs, which may or may not have 

 been inhabitants of deep water. One species, Dichelaspis orthogonia, habitat unknown, 

 was found "apparently" attached to a horny Coralline, which perhaps was procured from 

 a considerable depth. Two species were found attached to the skin of sea-snakes, and, 

 therefore, may be considered as surface-animals. 



N.B. — Small specimens of a Foraminifer (Discorbina ?) were found attached to the 

 capitulum of Dichelaspis sessilis. 



Megalasma, n. gen. 1 . 



Valves five, approximate ; carina extending only to the basal points of the terga, 

 with its lower end truncated and very wide. Scuta triangular, with their umbones at 

 a considerable distance from the rostral angle. Mandibles with four teeth ; maxdlae 

 slightly notched, with the lower part of the edge slightly prominent ; anterior ramus of 

 the first cirrus much thicker than the posterior ramus ; the two rami of the second cirrus 

 nearly equal ; caudal appendages uniarticulate, short and spinose at the extremity. 



This genus is nearly related to Pcecilasma. However, my reasons for separating it 

 from that genus are, I think, as important as those for separating Pcecilasma and Lepas, 

 or Pcecilasma and Dichelaspis. The new genus must be placed in the same Famdy as 

 these genera, being easily distinguished from them by the form of the scutum and the 

 width of the carina. With regard to the carina, Pcecilasma carinatum, which I described 

 on p. 44, shows a considerable resemblance to Megalasma; and to this affinity the 

 form of the scutum only partly opposes itself. For in Pcecilasma carinatum the basal 

 margin, which in Megalasma is totally wanting, has become a great deal shorter than 

 in the other species of the same genus ; so it seems that Pcecilasma leads to Megalasma 

 through Pcecilasma carinatum. 



The animal's body only slightly differs from that of Pcecilasma, the most remarkable 

 difference consisting in the unequal thickness of the rami of the first cirrus. 



As only one species of the new genus is known, I think it better not to enlarge upon 

 the description of the genus. Its habits and distribution will also be given under the 

 head of the species. 



1 From fityas, great, and sAau^a, plate or valve. 



