128 



L. HILLIS-COLINVAUX 



Fig. 37. H. scabra. Specimen from Florida, IX 1895, Curtiss. Scale bar is 2 cm. 



Ty'pe specimen. Florida, Sands Key, Howe 2905, 30 March, 1904 



(NY). 



Habitat. Growing on rocks from near low-tide line to at least 

 -20 m. 



Geographic distribution. North-western Atlantic. 



In general form and anatomy H. scabra is closely allied to H. tuna, 

 particularly to the somewhat modified plants of the Caribbean, and has 

 frequently been identified as tuna in herbaria. From this species it can 

 often be distinguished macroscopically by the rather bluish cast which 

 commonly occurs towards the apices of the branches, and by the rough 

 texture which results from the indurated spines which project from the 

 peripheral utricles, their length varying to a limited extent with the age 

 of the segment. When well developed, the spines are usually visible 

 with a good handlens. The relative ease of separation of the peripheral 

 utricles after decalcification and their small surface diameters are also 

 characteristic of this species, the latter averaging 42 [j,m in H. scabra 

 as opposed to 70 [j,m in H. tuna. Adjacent fused nodal units may remain 



