78 Studies on Arthropoda. I. 



Risso about 13 mm. long has a just perceptible, rudimentary 

 protuberance considerably behind the rostrum. 



In Spirontocaris microceros Kr. an area marked off by 

 a circular depression very near the base of the first dorsal 

 spine. 



In Bythocaris leucopis G. O. S. a distinct rudiment in the 

 keel a little behind the first spine. 



In Alpheus avarus F. a small, but well developed depression 

 a little or slightly behind the median keel. 



Palcsmon brasiliensis Hell., Pandalus Bonnieri Caull. and 

 Pontonia sp. have been inspected with negative result. 



10. Stomaiopoda. 



To begin with it may be remarked that moderately large to 

 very large specimens of the present order have frequently the 

 surface of the median part of the carapace more or less rubbed 

 and are consequently badly fit for the investigation, as in such 

 cases the dorsal organ is frequently difficult or impossible to 

 point out with certainty. 



The dorsal organ has been mentioned in descriptions and 

 besides shown in figures of some species of the genus Squilla 

 by at least two able Zoologists, viz. Stanley Kemp in his excellent 

 memoir on the Indo-Pacific forms of the order (1913) and by 

 Caiman (1917). They name it the "dorsal pit", which is only 

 a descriptive term, as they did not recognize what this pit 

 really is. It may also be pointed out that Giesbrecht in his 

 useful, extremely elaborate, long-winded and as to literature 

 not always very fair monograph of the Mediterranean Stomato- 

 poda (1910) has not observed the "dorsal pit", though it is con- 

 spicuous in the common Squilla mantis I,., at least sometimes 

 not difficult to see in 5. Desmarestii Risso, and ought at least 

 to have been indicated on his large figures of the carapace of 

 these two species. 



