588 THE VOYAGE OF H.M.S. CHALLENGES. 



and excavated to receive the extremity of the propodos. The second pair of pereiopoda 

 is slender, a little longer than the first, chelate, and has the carpos triarticulate. The 

 posterior three pairs of pereiopoda are short, slightly decrease in length posteriorly, 

 and have the dactylos " spinulose within." 



This diagnosis is drawn up after an examination of the type specimen of Hippolyte 

 varians in the British Museum, and from Leach's description, to which he adds, 

 " Montagu sent to me Hippolyte varians, the type of this genus," the definition of which 

 he gives as "Hippolyte rostro acuminato ante medium subtus bi-serrato; pone medium 

 et ad apicem supra uniserrato." 



The following additions to the above definition are taken from recent specimens which 

 have been found on the coasts of Devon and Cornwall. 



The mandible has the molar process at less than a right angle with the apophysis; 

 the psalistoma is reduced to a narrow process serrate on the inner margin, and the 

 synaphipod is wanting. 



The first pair of pereiopoda is stout and short, having the propodos articulating 

 with the carpos at the lower angle, a concave excavation being formed by the advanced 

 condition of the upper angle, in which hollow the extremity of the propodos lies when 

 the appendage is extended ; chela having the fingers subequal and hollow. The second 

 pair of pereiopoda is slender, and has the carpos triarticulate. 



Dr. Leach in his description of the genus says " carpo multi-articulato," but figures 

 the joint as triarticulate. The variance between the figure and the description 

 was probably due to the desire to bring other forms within the generic range. Thus 

 he has figured Hippolyte spinus, which he makes the type of a separate division of 

 the genus, with seven articuli to the carpos, so that the term multiarticulate was 

 intended to mean any number of articuli more than one. In 1865, in a report to the 

 British Association on the Marine Fauna of South Devon and Cornwall, the following: 

 passage written by myself occurs : — " Among the prawns we are enabled to add a new 

 genus to the British fauna, namely, Caridina of Professor Milne-Edwards. In making 

 this interesting addition we must remark that it is one of name only, since it is, we believe, 

 the same that Dr. Leach described under the name of Hippolyte varians, which has 

 remained misinterpreted. We have occasionally taken this species when dredging in 

 Plymouth Sound, but never so abundantly as of late. We have previously observed 

 the peculiar robust-looking first pair of pereiopoda, but it was not until recently we 

 observed that it had the peculiar structural formation peculiar to the genus Caridina, 

 in which the propodos articulates with the carpos, not at the centre, but at the infero- 

 anterior angle, and thus appears as a partially dislocated joint." 



The fact, however, that Leach made Hippolyte varians the type of the genus 

 Hippolyte, compels me to restore it to its original position, especially since Caridina 

 has only been recognised as a fresh-water form, and has the dorsal surface of the rostrum 



