[mcMURRICh] notes on SOME CRUSTACEAN FORMS 53 



shape, and, finally, posterior to the elongated plates is a group of 

 seven polygonal plates, which increase in size posteriorly, the two 

 that articulate with the outer and middle elongated plates being much 

 smaller than the others. Thus there are altogether fifty-one plates 

 composing this anterior portion of the carapace. 



The posterior portion terminates in a strong median spine, and 

 upon its border on each side bears three shorter spines or denticulations, 

 the most anterior of which, sometimes wanting, is situated opposite 

 the more posterior of the two linear plates that separate the two 

 portions of the carapace. The other two denticulations divide evenly 

 the interval between the anterior one and the base of the terminal 

 spine, the more anterior of the two being usually double. The plates 

 in this region are arranged as follows. Beginning posteriorly there 

 is a single plate, which bears the terminal spine, and in front of this 

 a relatively large plate with a convex anterior border which bears 

 near this border the almost circular anal region. Between this large 

 plate and the linear ones are two somewhat triangular plates and 

 finally there are two narrow marginal plates on either side, occupying 

 the intervals between the three lateral denticulations. There are 

 thus eight plates in this region and these with the two linear ones 

 make up a total of sixty-one for the entire carapace. 



The surfaces of the plates show a delicate sculpture which gives 

 them a faintly rugose appearance and at the anterior extremity of 

 each outer intermediate elongated plate there is a minute pore (s), 

 probably indicating the point of emergence of a sensory seta. 



In all the details of the arrangement of the plates, their sculptur- 

 ing, the position and number of the sensory pores and the form of the 

 carapace, there is practically identity with the description and figure 

 that Hansen has given of the younger stage of his ylV larva, and the 

 occurrence of its parent form, whatever this may be, on both sides of 

 the Atlantic seems to be an established fact. 



As regards the remaining parts of the larva little can be said. 

 The anterior part of the body is thin and gives the appearance of a 

 flat surface when viewed in profile. Towards the posterior part of this 

 region is a large naupliar eye (oc), situated beneath the fourth axial 

 plate of the carapace and, more posteriorly, corresponding to the region 

 at the level of the fifth and sixth axial plates, are the three naupliar 

 appendages and a well marked epistome. The details of structure 

 of the limbs were not made out, further than that the first pair were 

 uniramous and the second and third biramous, and all bore long setae 

 on their terminal portions, the setae of the mandibular pair extending 

 backwards almost to the posterior extremity of the carapace. Behind 

 the limb region the body forms a median band-like convexity, dis- 



