[15] DECAPODA FROM ALBATEOSS DREDGINGS. 359 



Pentacheles nanus, sp. nov. 



This species is very closely allied to P. sculptm aad will possibly 

 prove to be only a dwarf deep-water variety of it, but the distinctive 

 characters are well marked and very constant in all the large number 

 of specimens seen. 



The spines upon the carapax are much longer and more slender than 

 in P. sculptus and differ in number. Including the very long and slender 

 spine of the anterior angle, there are only five spines on the lateral 

 margin in front of the cervical suture each side, while there are normally 

 six in P. sculptus ; on the middle line of the gastric region back of the 

 two rostral spines there are, at nearly equal distances, first two single 

 spines, one behind the other, then a pair close together, and lastly a 

 single one, while in P. sculptus there is only one single spine between 

 the rostral spines and the pair ; the surface of the branchial region on 

 both sides of the sublateral carina is armed with many small spines or 

 spinules, and on the anterior part of the oblique ridge between the dorsal 

 and sublateral carinae there is one spine as large as the spines of the 

 sublateral carina itself, while in P. sculptus the surface of the branchial 

 region is unarmed and nearly smooth, except for the carinal and mar- 

 ginal spines. There is often a slender, horizontal median spine in front 

 just beneath the rostral spines, but this is not a constant character. 



The pleon is more deeply sculptured than in P. sculptus, and the dorsal 

 carina very much higher, the recurved carinal teeth of the third, fourth, 

 and fifth somites are very much' longer and more slender, and reach far 

 over the somites in front. The edges of the sulcated carina on the sixth 

 somite, instead of being low and uniform as in P. sculptus, are very high 

 and broken into several prominent teeth each side, with a stouter and 

 higher tooth at the posterior end of the sulcus. The edges of the pleura 

 of the second to the fifth somite are conspicuously armed with rather 

 widely separated short spiuiform teeth, while in P. sculptus they are 

 entirely smooth, or, in small specimens, inconspicuously armed with ob- 

 solete teeth. In place of the slight median elevation near the middle of 

 the telson of P. sculptus there is a sharp spiniform prominence, with oc- 

 casionally a smaller secondary one just back of it. 



In all the specimens seen the first perseopods (great chelipeds) are 

 considerably shorter than in P. sculptus, but these appendages are sub- 

 ject to so much individual variation in size that this will very likely not 

 prove a constant character. 



Males less than 50°^ in length are sexually adult, while in P. sculptus 

 males considerably larger than this are not adult, the first pleopods be- 

 ing very small and weak, and the secondary stylet at the base of the 

 inner ramus of the second pleopods only about half as long as the other 

 stylet. 



In the accompanying table measurements of five adult specimens of 

 this species and of a single immature specimen of P. sculptus are given 

 together. 



