;t '- 



--^- -.7:^--. !_::,- 



i>. 



HETEROCARPUS VICARIUS. 



149 



of the orbitj on a level Avith the base of the eye-stalky runs backward and 

 a little downward along about two fifths the length of the carapace^ then 



each side of the carapace. The uppermost of these, lettered a in the acconipanyiug cuts, begins at the pos- 

 terior boundary of the orbit, just behind the base of the eye-stalk, runs backward deliniug the lower limit of 

 the gastric and cardiac regions, and ends near the hind margin of the carapace just at the point wlicre the 

 hind margin curves backward to form tho hind margin of the branchiostcgitc. The middle lateral carina (d) 



Fig. 1. 



'Fig. 4. 



^:i 



t I J 





J 

 I 



Fig. 3. 



Fig. 5. 



Fig. 3. 



Fig. 6. 



/ 



\ 





originates anteriorly in the orbital spine and courses backward over the liepatic and branchial regions, below 

 carina a. The lowermost lateral carina (a) is continuous in front with the lower spine of the antero-lateral 

 border (the branehiostcgal spine of Stimpson), aiid sweeps backward below /; along tlie braucliial area until it 

 is lost near the hind border of the carapace. This complete expression of all the carimc is represented in the 

 first diagram (Fig. 1), Tt is realized in //. carhialus Smith (= //. ensifer, juv. ?), in wliicli all the carina; arc 

 developed throughout their whole course, although a is not so sharply defined on the anterior lialf of the cara- 

 pace as it is posteriorly. Still it can be followed quite up to the margin of the orbit. The next diagram 

 (Fig. 2) shows tho complete suppression of the anterior half of a. This coudition is exemplified in //. ensifer 

 A. M. Edw. In the majority of the known species, however, a is perfccll.y developed, while h is well-nigh 

 completely obsolete (Fig- 3). Wo then have two lateral carina. These are not homologous with the two 

 complete carina of E. ensifer, but with the upper half-cariua and iJic lowest one of that species. A sliglit ves- 

 tige of the anterior end of h appears in the form of a short ridge continued backward from the base of the 

 orbital spine. In this category come the following species : //. vicanus Fax., glhhosm Eatc, oryx A. M. 

 Edw., dorsalls Bate, alphonsi Bate, hostilis Fax., and affmis Fax. The next stage in the suppression of the 

 carina; is shown in Fig. 4, where, besides the absence of b, wc note the obsolescence of the posterior fourth 

 of c {II. Imvigatm Bate). In //. alexandri A. M. Edw., c has completely disappeared, leaving only one lateral 

 carina, a (Fig. 5). Finally, in //. la^vis A. M. Edw., all the carina; are obsolete (Fig. 6), and we have a 

 smooth carapace, as in Pandalus. 



The homology of these carina; has been misapprehended by some writers. A. Milne Edwards, for in- 

 stance, says that the superior lateral carina of //. ensifer is absent in II. oryx, whereas it is in fact the middle 

 one that is obsolete in the latter species. 



"a 



