Mr. C. Spence Bate on the Development of Pagurus. 115 
antenna is developed upon the brachyurous type; but the 
inferior has the squamiform appendage of the macrurous 
Crustacea. So have all the other appendages that pertain to 
the cephalon and pereion, except the last pair of pereiopoda; 
and these are not developed, at least they were not percep- 
tible to our examination—a circumstance that would accord 
with the animal being an undeveloped anomurous crusta- 
cean. The pleon and its appendages bear a very close resem- 
blance to those of the larva of a prawn, since it is equi- 
laterally developed and furnished with a pair of appendages, 
posteriorly and ventrally, attached to each somite, the last of 
which is much larger than the others, and is evidently a pro- 
gressive stage in the development of the great caudal plates of 
the macrurous Crustacea. 
We attribute it to the genus Pagurus rather than to any of 
our other anomurous Crustacea, because it differs from the 
known zoéa of Porcellana, and of that of Galathea we have no 
knowledge; but from the nearer approach of these last genera 
to each other in their adult stage than to Pagurus, we are in- 
clined to believe in a nearer resemblance of their larve. Hence 
our assumption that this present immature species is a young 
Pagurus. 
The next stage to which we allude (Pl. IX. fig. 3) is one 
which we noticed in our preliminary Report to the British 
Association. 
The animal is a small creature that was taken floating near 
the surface of the sea, in a warm day in June. Its general 
appearance is that of a young macrurous crustacean, and as 
such it has been classified near to Callianassa and Calliadina. 
It is symmetrical, except in the larger development of the 
great chela of the right side. The two succeeding pereiopoda 
are very long, but simple in their formation; the last two are 
considerably reduced in size, and the anterior terminates in a 
small imperfectly didactyle forceps,while the posterior has a 
copious terminal brush, consisting of cilia and short and broad 
spines, amongst which the short, obtuse, and spmous dactylos is 
discernible. The pleon is well developed, having each somite 
clearly defined, and all, except the first, carrying an equally 
developed pair of appendages, each of which consists of a 
peduncle and two unequal rami. The posterior pair, or uro- 
poda, differ from the others in having the peduncle shorter 
and the outer ramus longer and more robust; it is likewise 
slightly curved, in the older specimens, more on the left side 
than on the right. 
In this condition they probably continue until they find a 
suitable molluscous shell in which to reside. [ imagine that 
8 
