H. SECORIFRONS. 



Teeth on the carapace and upper mar- 

 gin of the rostrum all simple. 



Posterior eight teeth on the carapace 

 and rostrum nearly alike in size. 



Posterior dorsal centre of the third 

 segment obtuse. 



NATURAL HISTORY SOCIETY OF GLASGOW. 83 



Association. It has since been taken, about sixty miles off 

 Tynemoutli, and also at Berwick Bay, and recently another speci- 

 men was obtained by Mr G. S. Brady from a fishing-boat at 

 Sunderland. So far as the habits of the species have been 

 observed, it would seem chiefly to frequent deep water, often at 

 considerable distances from the shore. 



As the species may readily be mistaken for Hippolyte spinus, of 

 Sowerby, which it closely resembles, the following may be given 

 as the prominent distinguishing characters of each:— 



H. STINUS. 



Teeth on the carapace and upper mar- 

 gin of the rostrum all double serrated. 



Four posterior teeth on the carapace 

 are greatly larger than the teeth 

 anterior to them. 



Posterior dorsal centre produced back- 

 wards into a conspicuous tooth-like 

 process. 



I may here remark, however, that I find the spines of the cara- 

 pace and ro.strum are very unstable characters, requiring to be 

 coupled to others of more permanence to give them reliable value. 



In this same species the Eev. Alf. M. Norman gives figures of 

 seven different conditions of the teeth in the rostrum and carapace. 

 But with all the characters taken together, he establishes a good 

 •species in Hippolyte securifrons. The same inconstancy occurs in 

 the spines of the carapace of some of the Diastijlidce. 



Some time ago I exhibited at one of our meetings a specimen 

 of a five-spined Cuma; afterwards I found the same species 

 with one spine only, and others having two, three, four, five, and 

 up to seven spines, and individuals having, in addition to the 

 larger spines, a very minute serration along the central ridge of 

 the dorsal segments. Yet all these proved to be only variations 

 of one species, Cuma tri-spinosa, of Goodsir — a name that the 

 animal still enjoys on the good faith of the constancy of the three 

 spines. These irregularities of the rostrum are not confined to 

 the Macroura and Stomopoda, but are extended to the Decapods. 

 In the case of the velvet swimming crab, Porhmus puber, scarcely 

 two will be found with the frontal armature of the carapace alike. 

 Fortunately, in this instance, there are so many decided charac- 

 ters, that there is no way of getting wrong. 



I may further remark, that I find the terminal tail plate and 

 appendages in the Macroura and Stomopods much more constant 



